I played Tera about 10 years ago, when it was good.
Free market economy, free looting (anyone can get anything) with random distribution, and people could pass on them so the one who needs an item can get it. Everyone could exchange anything person-to-person. It's what made the "mmo" part for me.
There were tons of mechanics that allowed a medium geared person to outdo people with the best gear available - if you invested in crafting, for example, you could craft things that were otherwise unavailable (unless you bought them from someone) and if you used them properly you could smash anyone in PVP and single handedly do 5-7 person dungeons. One mistake and you were dead, though.
I loved the interactions with people. Some of the first moments were one guy who asked to resurrect him, he was just killed by a monster and was like "bro, pls, I don't want to walk all the way here again". So I ressed him, he added me to the friend list, we later went on a lot of hunts and dungeons.
Another time I was sneaking through pvp territory collecting some shit from enemy bases and I got killed by two randoms. They were surprised at my shit gear and said "yo, come back, we'll give you this stuff, we kinda feel bad :D". Went there thinking I'd get killed, but no, they helped and we also became friends.
At some point I was rich and bored and was just running PVP tournaments with my own virtual wealth. People fight, the winner gets 5,000 gold (decent sum) or some gear I had in storage.
Helped a lot of new people gear up, and they helped me.
Dungeons were fun when anyone could enter and re-enter. If someone died, we'd have to be very careful and kite/heal until they come back, and it was a thrill, we liked it. People were thankful for not being called dumb and being kicked. We even gave materials that they needed because they needed it more.
But people have changed these days. The playerbases seem to hate the above mentioned free trade. "oooh, what about real money trading?" "why does he get free gear from his guildmates?" "he gets help, I don't".
You needed to be friendly and work together, and the newcomers just didn't want that. They wanted a single player game with other players in it.
Not to "log in at 7pm EST so we can do X and Y". It wasn't even mandatory in most groups, just log in if you can, apologize if you can't.
But no, people wanted to just log in whenever and work on their own whatever.
Which is exactly what modern MMOs have become. Single player, heavily developer controlled games with a chat.