I have a pretty strong character in D4, I’ve spent some time farming items and leveling up Paragon, and I don’t feel like making a new character again. Since I usually play as a wizard, I’d essentially have to repeat the same process, and for what? Why can’t I do the season with my main character? I’d probably finish the seasonal quests faster, but at least I wouldn’t be so bored. I don’t know who came up with the “brilliant” idea that you have to create new characters, and now others are just repeating it. Of course, if someone likes playing like that, let them, but there should also be an option to play the way I described. For now, unfortunately, I had to stop playing because I’ve completed almost all the quests, and there’s really not much left to do.
You said it : “I had to stop playing because I’ve completed almost all the quests, and there’s really not much left to do.”. You pretty much summed up what happens with most ARPG : A lot of people get bored eventually, moreso than with other types of games, because there isn’t that much new content with each patch. I don’t know why it’s like that, but most ARPG players are bored when they keep their characters, not when they start anew. I know I’m like that : I need to start a new character, otherwise, I’m bored. I like trying new classes or at least a new build every season.
Anyway, as such, most ARPG are operating on that seasonal content as destroying content with one button is usually boring pretty fast otherwise for anyone who can play more than 10 hours a week. I’m never playing on eternal realms, so I don’t know how it works, but I guess that you cannot do the “Battle Pass” and that it is your main concern. If that’s the case, I understand, and I wish Blizzard would come up with a way for Eternal players to get the battle pass content (especially if they pay for said Battle Pass) without having to interact with seasonal content. Challenges could be tailored towards Eternal realms, with a higher power requirement and more grinding, I don’t know.
If it’s because you want to try the new Witch/seasonal powers, then no, it’s pretty much like playing a beta so it’s nice that it’s separate from the Eternal realm. You can hate the concept, but Battle Pass aside, no one is forcing you to participate in seasonal content. Some of these seasonal powers could come back in one form or another in the next seasons (aspects, unique items, etc.), but most people come back to start anew, not to try the new powers per se. For Blizzard, it’s one way to bring people back each season (and Blizzard wants them to play more than 10 hours every 3 months).
You’re right. However, I don’t like it. I would just like to log in every season for a few, maybe several hours, see what’s new in the season, and if there are any quests, do them. Maybe farm something new and that’s it. I understand that different players in games can have different goals, but why can’t there be a choice? They won’t convince me to play seasonal characters. I’ve already uninstalled D4 and am playing another game now, and I’ll probably only return to D4 with the next DLC, unless I decide it’s not worth it anymore.
You made the right decision.
Seasonal content is what the majority of people enjoy in ARPGs right now, and I’d say the last ten years have been like that. People love going into a new season with a fresh perspective, exploring new builds, discovering new things, and experiencing gameplay changes.
What you prefer is something that MMOs provide much better!
One character for all eternity.
WoW is like that—why aren’t you playing that game, for example? I’ve had my Paladin forever, still progressing through every new expansion and patch on that character, and only continuing to grow.
I play ESO, and I also have a mage character there. I’ve played all the Diablo games, including the expansions, and I’d like to keep doing that. In D3, I tried a seasonal character once and didn’t want to bother with it again – it felt like a waste of time to level up again, etc. Also, I really like my character and don’t want to make a new one – I’ve invested a lot of time into it, I’ve even taken her through Hell 
, so I don’t want to start a new one now. I don’t like that even though I paid for the game and the expansion, I can’t use certain game content with my character. But as I mentioned earlier, I’ve uninstalled the game (I saw a video about the new season, and that’s why I’m commenting). There are other games. On the other hand, if Blizzard actually cared about the players, they’d provide such an option too. Unless it’s just me who has a problem with it 
They could release seasonal content on eternal realm for the last month of each season to bring back some activity for those that just want to play around with it without starting new characters.