I would go a step further and say that the games that were great back then wouldn't be great now. All these games have been re-released and remastered, and while people play the MP, they don't stick.
I was watching Youtubers play Halo 3 (the one I happened to play the most) and the nostalgia was great. Did I actually fire up Halo 3 to play though? Nope. The 10 minutes watching someone else play was all I needed. That's when it hit me.
I think I want a Halo MP game, but I really don't. I played 5, but not a bunch. It was a solid game. Other games are better. I will tell you how much I hate COD and Warzone and how the skill based matchmaking is garbage, but I played the heck out of it all weekend anyway.
Gamers are chasing nostalgia, and we're never going to find it on the MP side. If they innovate, they break the formula. If they don't innovate, nobody will like it because it isn't really what they want.
I hope I'm wrong, because I want to like Halo MP, but I don't think I really know what I want.