Unless the artists self-financed it and didn't make contracts with record labels, it basically is work for hire.
Lets take game series as examples - even if your studio created the game and the franchise, the IP rights to the name, characters etc belong to the publisher as they financed it and that was the deal made with the studio. Unless they make a deal with the publisher, they also cannot just leave and continue using that same name under another publisher. On the other hand, the publisher has the right to use the name even if they hire a new studio the make it. This is the case with Call of Duty series too. It's basically work for hire, and it's a decision creators make when thinking if they could finance it on their own or if they need a publisher to finance the initial creating part. Since publisher takes a risk, they also get to own the work done.
It's the same thing when you work for a software company as coder. You don't own the product or the code you made, as you were hired to do it for the company. If you want to keep it all to yourself (and also get larger rewards), you need to finance and handle all parts of it yourself.