As I remember it, it was a bit of a douche move by Tridgell, driven by a Stallman-like free software ideology.
Is the benefit clearly obvious? If you actually adhere 100% to Stallman's code I'm not so sure.
In fact, it was the reverse - he felt like he was being locked out of kernel development because he didn't want to align his moral code with those who used BK.
So, he tried to find a way to hold true to his code without forcing the rest of the kernel team to give up BK.
You say that like it's a bad thing.