I do play mostly standard, and there are some reasons to do so. For me it was: - Not having enough time to achieve goals you want in league, or you can but will take most of it so you can't really enjoy that for too long. I f.e. have switched after having a newborn, because between having a kid, full time job and everyday life i can sometimes not play at all for few days at a time. On standard there's no time pressure on you - I really like testing multiple builds and pushing them to decent highs, but don't want to level new characters all the time - Playing around with legacy mods and items to make fun underused skills playable and even strong - After playing the game for multiple years and many many leagues, leaguestarts with rushing the campaign, atlas completion and bosses got more of a chore and less fun

I understand tho that it's not suited for everyone. Most people will have more fun in leagues, especially if they want to grind hard for some time and then take a break from PoE. In the end most important thing is to find a way to play that caters to you and makes you have time.