I'm sure a lot of people are familiar with the meme:
"Tradition is just peer pressure from dead people."
I tried playing with a 4 color deck for a bit, but I find myself sticking with 2 color decks myself. I don't know, perhaps it is just tradition, but maybe I just like how it looks better. 4 color decks look kind of clown-like to me. When I tried using a 4 color deck, it kind of wore off and seemed like the "new normal" but then I pulled out my 2 color decks of cards and I was like: "oh my, that was so weird, the 2 color deck looks so much better: excuse me a moment while I go wash my eyes."
Needless to say, I haven't gone back to 4 color deck since.
p.s. For those I know will ask, I experimented with a 4 color deck for about a week, but yeah, I'm sticking with 2 colors for now.