I became active on SO late (2018) and now have 6K reputation. Providing good answers to new questions was worth basically nothing. No one upvotes you.

90%+ of the upvotes come from super old questions that have been around forever. Google indexed them and sent traffic there. Old inactive accounts get 1000s of upvotes a day and if you weren’t active when Python 3 was new or when Apple released Swift or whatever then trying to build reputation felt like a waste of time.

Contrast that with Reddit: commenting on new posts is the only way to build karma. It incentivizes new activity.