Also, a lot of players weren't around when those fights were relevant.
There already exist methods of doing these older fights closer to the "originally intended" level. It's up to the players whether or not to make use of those methods.

Because they don't want players to outlevel and outgear those fights like the old ones,
That's... kind of what happens in a vertical-progression MMO, though. They literally made the game to be this way.

idk though, I'm just not really a fan of the whole FOMO thing. With seasonal events and such, it's acceptable, but I don't want to see it in actual game content.