Or, that's how you see them.
In reality, these guys have built a character over the years. For MVP, it happens to be in the WWE and it happens to be the baller gimmick. For others, it was elsewhere.
Let me ask you this: was Ric Flair's character changed when he jumped to the WWE? How about Rob Van Dam? I'm also pretty sure Goldberg stayed the same, and it also goes for Scott Steiner. In fact, WWE was so used to the characters other companies developed, that when Nash, Pac and Hall came back, they were no longer Diesel, 1-2-3 Kid and Razor Ramon. Going further, Chris Jericho remained the same, and so did Rey Mysterio.
Obviously, I can continue with this for days. I can also list all the people who WWE changed when they came in. Some of them were successful, such as Steve Austin, and some of them bombed, such as DDP.
The point is that there is nothing wrong with maintaining someone's character and preserving its value. When an MVP debuts, people expect MVP. So they expect the song, the look, the name and the gimmick. Those are his selling values, that's what makes this signing important. Why would you change that? It will further confuse your fans and insult their intelligence. It's not 1993 anymore. Why would you strip a wrestler of all that he is perceived as? Just to please a couple of douchebags on the Internet?
What would've happened if MVP came out as something different, with a totally different name and a theme song? Disaster.
Plus, you're thinking of all of this in a negative way. What fan out there went "Oh, fuck that, he's the same as he used to be in the WWE. I will never watch this program again". No one ever has, no one ever will. It's just some bullshit IWC standard that everything has to be unique and adapted to the company.
It doesn't. Not always.