[Q] Validators & Lido

I am aware about the centralized & risk of Lido staking.

But couldn't grasp the drawback of centralizing the nodes on Lido?

One of the point is about how Lido isn't decentralizing in term of "node operators" as Rocket pool

I couldn't understand that.

How does lido has low numbers of Validator nodes But at the same time keeping the normal APR of 32 eth?

I am a little confused about the matter.