It’s the same reason a company might hire an outside firm to do penetration testing, rather than ask its head of cyber security, “Hey why don’t you conduct a test to see if you are doing an awesome job, as we need to figure out whether to fire you or give you more money”.
outsourced contractors will tell you what you pay them to tell you
of course all that depends on the contractor, who’s doing the hiring, and the industry etc
but the point is, just because it’s outsourced doesn’t mean the incentive structure will “work” any better than internally
I assume this is like one department of a company using Azure and the other using AWS because nobody wants to share their turf. Writing a check is easier than talking to your coworkers.