I'm able to search chats on my phone and PC and go to that message when I search, and get all the context around it. Even messages that are several years old. I just tested it. Maybe it's just your Teams settings?
So I donno, perhaps it's something funky with our Teams deployment, but this is such a basic feature that I have a hard time understanding how it could ever be implemented this way. Certainly no other chat service I've used has had this kind of problem.