I think thats the main rub, think about the maintainers. Using a bespoke test framework, is often a way of introducing conflict, no matter how good a coder you are. As Jeff Atwood says, imagine the maintainer being a psychopath..
https://blog.codinghorror.com/coding-for-violent-psychopaths...
Would you rather have your psychopath stalkers tearing their hair out over the Boost dependency you dragged in? Once written it stays mostly the same, there is not much to maintain. I can't see why rolling your own framework would introduce conflicts; unless you're in an environment where writing code to solve problems is frowned upon, but then you have worse problems.