>>534112023
In SA1 Sonic couldn't stop Chaos from destroying Station Square leading to a bittersweet but hopeful ending; since SA1, most 3d mainline Sonic games since then usually have conditional good endings that require some sort of sacrifice

This isn't a bad thing, in fact I'd would say it's a major part of what made dark age Modern Sonic so compelling, but it also kind of explains why things like Prime's ending happen