A couple of weeks ago, a newer member of my era guild asked on Discord what it was that kept people playing Classic era. Surely everyone had "done it all" multiple times over by this point. I found people's responses very interesting to read.
The question of why one should invest in an MMO that isn't going to receive any more content updates is one I've seen brought up many times before - heck, people were raising it in the run-up to Classic, before it was confirmed that there was going to be progression into Burning Crusade.
Honestly, I've always found that concern a bit weird. I get that new content is exciting, and that a big update always generates a lot of interest, but surely you don't specifically play to experience some unknown future updates? I thought we played because we were enjoying the here and now? People revisit old games, films and books all the time, and you wouldn't consider that strange just because there isn't a sequel in the works, would you?
Often there seems to be a worry of getting invested in a game in which you might eventually run out of things to do, but this is coming from the same people who rarely spend more than a month at a time in any new MMO anyway. If you're having fun now, why does it matter? Running out of things to do is a problem for much, much later, not to mention that most people get bored before they've done everything anyway.
In addition, I think many people who ask these kinds of questions overestimate how much time everyone else spends playing. Let's assume it takes about ten days /played to level a character to 60 in OG Classic. (Yes, I know it can be done faster, but let's assume a more casual approach that isn't super-optimised and includes some idling as well as spending time on non-levelling activities such as professions.) Even if you play forty hours a week, levelling a single character to 60 will take you six weeks. If you play twenty hours a week, it'll be three months. If you take things super casually and only play four hours each weekend, it will take you over a year just to level a single character from one to 60, and at that point you haven't even touched endgame or created a single alt. Suddenly it shouldn't sound so strange that there are plenty of people who weren't "done" with Classic by the time it progressed into Burning Crusade, considering that it lasted for less than two years in total. Era provides a home for those who couldn't keep up with that pace but still wanted to keep playing.
And there are things that era offers that you can't get in any other version of WoW. I personally didn't mind the themes of Burning Crusade, but if you liked Warcraft in its original, mostly traditional fantasy state (without space goats etc.), it doesn't get any closer to that than Classic era. It's also "sandboxy" enough that people are pretty good at coming up with their own challenges and making their own content. There's a server community on era that's closer to the way community worked in Vanilla than you'll find anywhere in current Classic. And I know many people hated 40-man raids, but some weirdos (like me) really liked the bigger raid sizes and you can't get those in any other version of WoW either.
I have to say that even without further updates, I'm really not worried about running out of things to do in Classic era. I have limited hours to play and don't spend them solely on WoW, so just looking at my current stable of characters I feel like just levelling and gearing them all is something that could keep me busy for many years to come. And if I do eventually get bored of it... so what? If Blizzard stick to their plan of maintaining era indefinitely, I can just take a break and come back to it later whenever the nostalgia cravings hit me. Unlike in a progressive MMO, taking a break won't mean that on returning you discover that suddenly, everything is different and you're massively behind. For some of us, that's a feature, not a bug.
And yes, I did it again.