Spoiler Alert: This story includes a lot of insights from the AOT Manga. If you haven’t read it, This is your last chance to back off.
Well, there are a lot of things that Eren did, for example killing 80% of humanity, turning people into titans, destroying Marley and the list goes on.
But also, in the end, Eren did nothing. Like do you believe Eren was someone who could’ve been killed off easily?
A person who started the rumbling that killed millions of people with enormous titans backing him up would die that easily?
The truth is Eren allowed the Survey Corps and Mikasa to kill him.
If they hadn’t killed him, Eren would’ve destroyed the whole of humanity.
Even though he knew there was a possible way that he could survive and the rumbling could be stopped, Eren didn’t plan on changing the future that was planned for him.
He was stuck in his past, present, and future and this was the reason why he didn’t do anything in his last moments.