> Was it the specter of lawsuits (which ultimately had no effect?)
I think that this was mostly it.
> Was it GPL vs. permissive licensing (which seems like it would favor BSD in terms of adoption?)
Many folks prefer to adopt & contribute to an OS when they know that they are legally protected from others taking their contributions proprietary.
I think that another factor, sadly more important in the 90s than now, is that the GNU userland was far more user-oriented than the BSD userland. Back then, Unix users actually used the command-line tools, and GNU was in a lot of ways more pleasant (if also, um, a bit scattershot and buggy).
I think that this was mostly it.
> Was it GPL vs. permissive licensing (which seems like it would favor BSD in terms of adoption?)
Many folks prefer to adopt & contribute to an OS when they know that they are legally protected from others taking their contributions proprietary.
I think that another factor, sadly more important in the 90s than now, is that the GNU userland was far more user-oriented than the BSD userland. Back then, Unix users actually used the command-line tools, and GNU was in a lot of ways more pleasant (if also, um, a bit scattershot and buggy).