Mopar Performance Roller Rockers

I do like how they are bushed instead of needle bearings.

I was going to say that too. And the way the bushings are grooved will help distribute the oil film, similar to what the grooved shafts do.

What is the reason everyone is wanting the bushings on a rocker arm that has an aluminum body?

Aluminum alone is in general a poor performer as a plain bearing material compared to bronze or other materials. You will never see a aluminum used to bush a steel part unless there was no other option or the person doing the work didn't know better. Will it work, maybe/probably. Is it a better choice than bronze? Absolutely not.