Yes that's also what I'm talking about
Your previous characters aren't important anymore, it's a fresh start all the time. On each new season there has been 0 previous time and effort investment
You have on the game as a whole, though. Mechanics, strategies, locations, weapons, lore, maybe friendships with other players. Hard to leave all that behind.
Diablo seasons are just a character reset for those who enjoy them. It's a huge part of a lot of ARPGs like Path of Exile or Diablo. As you can reach endgame in about 5 hours on diablo and have your complete build in 20, it makes sense.
Enforces everyone to reset at the same time and not use gear and stuff from previous characters. Some people care about leaderboards and those usually reset at the same time. For other ARPGs with a trade economy that being reset is often the biggest draw, but that doesn't apply to D3.
I couldn't give less of a fuck about leaderboards, but I enjoy seasons in D3, but not D4. In D3 you get to max level and get a set of pretty good gear in a few hours. I'm a casual player, I don't play the entirety of the season because I kinda hit my limit and stop getting new shiny things and don't feel like pushing it so I stop playing. Then a new season comes out, I'm like "I haven't played Diablo in a bit, that sounds fun" and I do the same thing, smash monsters and get shiny things.
In D4 the new season landed and I just couldn't be bothered to level again and it really killed the game for me, I'm kinda maxed out on non-seasonal, it gets to the point where you're doing the same thing over and over for hours, or you push harder content where it takes forever to kill something and everything kills you in one hit. I just want to smash shit and get loot, I don't want to level again if it takes more than a couple hours.
Basically seasons can be fun (also they test new content, that keeps things fresh) as long as you can jump right back into the game. Without it you have a ton of legendary items for every class so you just never really need new gear, you just grind for that single piece you need for a 2% upgrade.
Tldr I don't want to grind, I just want to smash baddies, and I'm basically a bird collecting shiny shit. D3 enables that, D4 doesn't. It's all about implementation.