Was the problem just in the different approaches between Stallman and Torvalds? That being: Stallman wanted to create GNU from the outside in (editors, then tools, then compilers, then the kernel) whereas Torvalds went inside-out?
A new editor or a new command-line tool was immediately useful to a user of a proprietary Unix.
In contrast, a new kernel would not have been useful to the user of a proprietary application or a proprietary command-line tool unless perhaps pains were taken to give the new kernel binary compatibility with proprietary kernels -- and even then there would have been worries about whether the user had the legal right to run the proprietary tool on the new kernel.
In summary, the order in which Stallman chose to build the pieces was the order that grew the user base the fastest, which in turn grew contributions from developers the fastest, in a virtuous cycle.
In some ways you could argue Stallman's approach was disrupted by the arrival of cheaper commodity hardware.
Linus also benefited tremendously from having the GNU toolchain and userspace already available.
I'm pretty sure no one could build a functioning micro-kernel that'd be useful and able to compete at the time the Hurd project was still relevant. Then again, maybe I'm just making excuses for the FSF.
People weren't really clamoring for Hurd or a kernel for GNU, because they got an OS with their computer, and got the GNU tools and libc. The really major geeks would buy old, used workstations, which were built like tanks and were plenty fast for running single-user unix.