There are a few exceptions, but overall the BSDs have very well engineered and maintainable code. They don’t move as fast as Linux distros do partly due to less manpower and partly due to taking the time to do it the right way. There is much less churn and they don’t have the cruft of supporting obscure UNIX flavors that have faded into distant memory like GNU utilities do. Take a look at some FreeBSD code and their GNU and Linux equivalents and you’ll see what I’m talking about.