Why is the author of the Book of Hebrews not talking about the restoration of the modern State of Israel?
Because the author is talking about going to heaven when Christians die, which is rest from the life in this world, And the importance of faith, in holding to that promise. So he gave Abel, Enoch, Noah, Abraham, and Sarah as examples in Hebrews 11, of having faith.
You have to go back to Hebrews 4, as he works up to Hebrews 11. In these verses, he is talking about Jesus's rest, and the promise of believers entering the same.
1 Let us therefore fear, lest, a promise being left
us of entering into his rest, any of you should seem to come short of it.
2 For unto us was the gospel preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard
it.
The author, who I assume to be Paul,in verse 2, is saying the gospel was preached to the Jews, but (in Hebrews 3) like that first generation coming out of Egypt,
did not have faith (because they feared the giants in the land) that God would make it happen anyway, they did not enter the promised land. Which he is using entry in the promised land as an analogy. So the Jews by rejecting the gospel, don't get the reward of the gospel of Salvation because they didn't believe it.
So Paul is going through on the importance of having faith and keeping faith to reach the end results of our Salvation. That's what Hebrews is about - our Salvation, keeping the faith, to enter heaven, and to inherit the Kingdom of God.
Paul made the same comment as Peter and John (in Revelation) essentially, that this world and everything in it will be destroyed, and of a new heaven and new earth forthcoming.
Hebrews 1:
8 But unto the Son
he saith, Thy throne, O God,
is for ever and ever: a sceptre of righteousness
is the sceptre of thy kingdom.
9 Thou hast loved righteousness, and hated iniquity; therefore God,
even thy God, hath anointed thee with the oil of gladness above thy fellows.
10 And, Thou, Lord, in the beginning hast laid the foundation of the earth; and the heavens are the works of thine hands:
11 They shall perish;
but thou remainest; and
they all shall wax old as doth a garment;
12 And
as a vesture shalt thou fold them up, [same as in Revelation 6, sixth seal] and they shall be changed [Revelation 21]: but thou art the same, and thy years shall not fail.
So Hebrews 11 is not about the restoration of Israel. But is part of the overall message of Hebrews to keep the faith.
