Why do you think they're not? I know most people tend to compartmentalize with a reductionist approach, and they can;t see the forest for the trees. The bible is consistent, since there were those 144,000 sanctified saints from the 12 tribes in ch. 07, of course they are the same group in ch. 14, there's no reason to suspect otherwise, if you do it only gets things complicated and get yourself confused.
I believe two different groups are revealed with the number of perfection associated with them.
Chapter 7 - 144,000 of the twelve tribes of Israel.
Chapter 14 - 144,000 Firstfruits who follow the Lamb alive into heaven before the GT.
Revelation is a book of climax of both Old Testament promises and New Testament promises.
Many dear Christians tend to give most of the weight in Revelation to fulfillment of New Testament promises to the church.
I would encourage such to be enlarged some. Revelation also concludes some matters related to old covenant Israel.
As God reserved for Himself in Elijah's time 7,000 who had not bowed the knee to Baal,
similarly the vision of a remnant from the 12 tribes indicates God's preservation of national Israel THROUGH the GT.
While some believers move to the conclusion that these 144,000 Jews will be great evangelists, nothing at all
is said about thier activity. We only see that they are selected to be preserved.
The flavor of their preservation has more of an Old Testament tone than the flavor of the 144,000 FIrstfruits in chapter 14.
1.) The directions to seal them comes not from the Lamb but from
"another Angel" (v.7:2). While here as well as other places
in Revelation "Another Angel" should mean Christ. BUT He is designated like His Old Testament manifestation as "the Angel of Jehovah."
IMO the flavor is of Christ in His old covenant characteristics keeping promise to the Israelites.
(See Gen. 22:11-12; Exo. 3:2-6; Judges 6:11-24; Zech. 1:11-12; 2:8-11; 3:1-7).
2.) In contrast to this the manifestation of Christ in chapter 14 is more related to the new covenant "the Lamb" (14: 1,4)
3.) Where as the 144,000 sealed in chapter 7 are preserved by "the seal of the living God" (7:2) the 144,000 of chapter 14
are related to "His [the Lamb's] name and the name of His Father".
4.) Whereas the 144,000 of chapter 7 are referred to as "the slaves of our God"(7:3) the more intimate life relationship
of the Firstfruits in chapter 14 is to "His [the Lamb's] Father" (14:1)
Both groups are assured ownership by God as the mark of preservation is on their foreheads.
5.) Just taking what we are told in the two respective chapters ALL WE KNOW . . . is the Jews are preserved and Firstfruits are raptured.
That the 144,000 Jews are great end time evangelists is only speculation.
And it is usually based on the faulty assumption that NO gospel preaching Christians will be LEFT on the earth
after a pre-great tribulation rapture of the whole church.
That the 144,000 of the twelve tribes in chapter 7 are latter raptured to stand with Christ on some heavenly Mount Zion in chapter 14
is also speculation. Most likely it is based on God using the same number signifying
a.) a remnant
b.) perfection of some sort.
6.) All we are TOLD from chapter 7 is that these 144,000 are sealed that they be not harmed by the damaging of the judging four winds
during the GT. Speculate if you wish that they are SEALED in addition that they may be raptured. It just says they are sealed to be protected.
And I saw another Angel ascending from the rising of the sun, having the seal of the living God; and He cried with a loud voice to the four angels to whom authority was given to harm the earth and the sea,
Saying, Do not harm the earth or the sea or the trees until we seal the slaves of our God upon their foreheads. (7:2,3)
7.) In fact in chapter 7 we are told NOTHING about their spiritual condition. We are only told that the living God has
SEALED them for protection and preservation.
In contrast the 144,000 Firstfruits of chapter 14 are followers of the Lamb where ever He goes. They being redeemed from the earth (raptured)
are for the Lamb and the Father's satisfaction. They are a testimony to thier being a pleasure to the Father and the Son.
8.) During the great tribulation we are told that TWO classes of people will stand against the persecution of the Antichrist.
1.) Those
who keep the commandments of God.
2.) Those who
have the testimony of Jesus. (Or those who have "the faith of Jesus." )
And the dragon became angry with the woman and went away to make war with the rest of her seed, who keep the commandments of God and have the testimony of Jesus. (Rev. 12:17)
Here is the endurance of the saints, those who keep the commandments of God and the faith of Jesus. (Rev. 14:12)
This does not mean that the Jews on earth at that time are successful in keeping all the commandments.
I think it means that they DO resist Antichrist by keeping the commandment that no other god can replace the God of Israel.
Also in Revelation 12 and 14 though in one sense the two groups are distinct, they are also seen as one entity.
1.)
"the rest of her seed" of the persecuted bright woman of light.
(12:17)
2.)
"the saints" (14:12)
During the 3.5 year great tribulation especially monotheistic Jews undergo persecution and monotheistic Christians also.
Some might pushback saying Christians must keep the commandments of God once they have the faith of Jesus.
However, I think the order in that case would reflect this by putting
"the faith of Jesus" or
"the testimony of Jesus" BEFORE
"keep the commandments of God."
I'll let you consider these points before writing more.
Bottom line is that I would teach perfection of preservation is over a remnant of the twelve tribes through the GT.
And a perfection of pleasingness in following Christ causes
some living believers to be rapture as Firstfruits
EARLY
before the start of the GT.