Frontend bugs mostly stem from usage of overblown frontend frameworks, that try to abstract from the basics of the web too much. When relying on browser defaults and web standards, proper semantic HTML and sane CSS usage, the scope of things that can go wrong is limited.

It's pretty wild that this is the case now (if it indeed is), given that for a long, long time, sticking to sane, standard stuff was the exact way you'd land in a glitch/compatibility hell. Yes, thanks mostly to IE, but still.