Does it say exactly what he preached to them?
Now you are admitting that you don't know.
It doesn't matter though, because just the idea that he preached to them tells me that he intended to give them knowledge that they did not possess, hence he taught them. If Jesus taught them something, was it for their good? I would think so, otherwise why preach to them?
And He announced to them that He had completed what He came to do. He didn't say, "It's time to repent."
I do not believe that he made his way to the spirits in prison to announce that he had completed what He came to do, and turned away from them and said good-bye, I know there are many of you who do not have any idea who I am, but that was your fault for being born at the wrong time, in the wrong place, I can do nothing for you, but I did want you to know that I have complete my mission. Sorry it didn't work out for you. That is not Jesus's style.
They are in prison instead of in Abraham's bosom.
1. You don't know God's thoughts or ways.
2. People aren't at fault for when and where they are born. Those decisions belong to God.
Acts 17
26 “And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation;”
3. Jesus doesn't say, "Sorry it didn't work out for you."
Romans 1
18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness;
19 Because that which may be known of God is manifest in them; for God hath shewed it unto them.
20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:
We know God is just and omniscient. He doesn't judge unfairly. You're painting a false picture.
Hebrews 9
27 And as it is appointed unto men once to die, but after this the judgment:
Men don't die and then accomplish something before judgment. You can't squeeze men's words in between God's words.