The pretty obvious reason in my opinion: Ethereum's fees have been quite high for a while, and Binance Smart Chain(BSC)'s fees are drastically lower. And yes, BSC is like magnitudes more centralized than Ethereum, but it comes to show how a lot of people don't care that much if a certain project is decentralization or not as long as they can make their bets on certain tokens.
The BNB coins has grown exponentially and i hope it can maintain this growth and do not dump as quickly as pumped. Since the BSC is getting attention, does it means that the projects on BSC like Pancakeswap (CAKE) , Sparta, Bake etc will also get big returns ? Those who missed the gains in bnb , can invest in these projects for good profit.
Binance is the first who is using the eth problems with fees in their advantages. And it's paying off big for them. I hope they can keep the website and app working smooth without slowing down with this many new people coming in.