Getting ratings and entertaining people are two different things and ratings stunts can backfire if people aren't impressed with what they're watching.Yes, to get ratings is how TV shows stay on the air. That's how this business works. It's the first rule in the TOS bible is to entertain a certain number of viewers or they don't stay on the air.
This is a business process, not a charity, not a philosophical treatise. It is meant to get ratings and to bring in viewers.
And it succeeded.
That said, I don't really get how Star Trek characters coming back to Star Trek bothers people so much. They're Star Trek characters, it's Star Trek, the show about Star Trek characters!