A lot of big projects have amazing longevity to their older architectural decisions. Unreal still has a lot of stuff in it people that used UE1 would recognize, I did most of my professional development on UE3 and a bunch of that is still pretty recognizable. Similarly Chrome is a product of the time it was first created. And looking into the Windows source is probably like staring into the stygian abyss.

There is a lot of legacy and tech debt out there!