Why didn't Ethereum build dPOS directly into the protocol if so many people delegate their stake anyway?

I operate a Rocket Pool node and I'm honestly just trying to understand what the disadvantage is of a dPoS system. It seems like if anything the current design has led to worse centralization because so many people use centralized exchanges, giving up complete control of their stake.

It makes sense that dPOS where validators don't need to have any stake is problematic, but what about a Rocket Pool-like system where stakes can only be delegated as much as the validator themselves have staked directly? Wouldn't that just cut out a lot of the middle complexity while enabling people to stake without giving their private keys to a centralized staker?

You could even increase or decrease validator's cuts rewards based on the size of the waiting pool of Ethereum delegated to be stakers.

I just feel like I don't understand the technical reasons for the 32ETH staker system, it feels unnecessarily convoluted, and has led to more centralization. Anyone care to enlighten me?