Stack Overflow rarely surfaced a solution to your particular problem, but solutions to tangential or otherwise very similar problems. You still had to reason around the posters problem context and try to see if it really matched your own. You still had to have some understanding.

LLMs present a solution as if it is 100% in the context of your problem. You arrive at a solution without being forced to think at all if the solution applies to your problem.

Without being forced to, many will not. I teach programming and I can tell you it is so so obvious when students are just blasting shit from ChatGPT into their submissions without thought.