Sometimes the platform team is staffed by people that have been there forever, as a sort of semi-promotion. But when they know everything, it's easy to have little interest in the difficulties of learning internal concepts: After all, the learning has already been done. This makes the tools be technically capable, and intractable. Other times, the team is easy to get along with, but what they deliver isn't very good at all, and the lack of quality is papered with social skills.
You need people capable of understanding the problem other teams have, and their architectural constraints, and deliver something that will save them time, and they'll prefer to use over some open sourced hodgepodge. They need to think of upgrade paths, or live in a low-repo environment where the platform team can upgrade things for everyone. The customer service attitude should be immaculate, as to make people be happy to ask for help, yet be so good at documentation, or at simple enough architecture, as to make that customer service load be light. Many places can't hire people that meet those kinds of profiles at all, as someone like that will basically excel in most roles in most companies. So yes, you end up with the technically capable, yet gruff guys that nobody wants to talk to: The equivalent of Seinfeld's Soup Nazi... and that's if at least they are very good.
Most team topologies will work if your company is full of empathetic heroes though, so platform teams might not even be needed if you really are that good at hiring.