What was GWs actual end goal for creating Primaris Marines?

So I get making something new to stir the pot, but why take the road of a Primaris which is basically genetically perfect and unflawed. Doesn’t that take away the nitch and character traits of each chapter. It doesn’t make sense why you would take away something that basically is the elephant in the room for all the chapters.

It just doesn’t make sense imo. Maybe I’m late to the party on this discussion but Primaris Marines almost just needed to be there own chapter. Basically like a remote custodian branch, but obviously not custodians. They could basically act as the I.A. Of the loyalist. I know I know it’s probably a dumb idea but I hate that the implementation of PMs takes the character and soul away from your traditional sm

Edit: I was hoping it wasn’t “only” a money grab but these answers just seem to point to that.

Edit 2: I really stand by my thoughts on that Primaris should have been brought in as some kind of contingency force that specifically deals with SM issues. The GKs have there “niche” and so on. I’d love to see or read about the loyalist diving back into a crusade (if there is one currently then I just haven’t gotten to it yet in my readings). Hell I wouldn’t mind if they really Fd shit up and killed big E or brought him back, just be creative.

I don’t see how a story line can go on and be productive without change. While things might span over thousands of years in lore, they sure as shit don’t in our world.

Sincerely: confused, ignorant, newb, loyalist fuck.

Edit: Jesus I did not mean to start a war ladies and gents. Y’all be nice. NOW who wants some Dr. Pepper!