Cost was not the only problem with Minix, although it was pretty hefty (it would have been about $180 in todays dollars for me in the UK). For students (as both I and Linus were) that was a lot of money.
AST was firmly of the belief in Minix as being educational code, and hence only accepted patches along those lines. I don't remember if there was copyright assignment too, but there must have been something similar. This was at odds with the people who wanted to use Minix as their operating system.
For example the Minix of the time only supported 16 bit mode on x86 which meant no memory protection and only using about half a megabyte of memory on multi-megabyte machines. Someone produced fairly large patches that let it work in 32 bit mode, but they were never distributed as part of Minix because they didn't further the education goal (more code, harder to read and understand etc).
Another example was that the filesystem code was single threaded and only handled one request at a time. This meant easy to read and understand code, but dismal performance. Again this hindered those trying to use Minix versus those learning from it. This was such an issue that the original Linux announcement has this line:
PS. Yes – it’s free of any minix code, and it has a multi-threaded fs.
Essentially Minix wasn't seriously usable, cost a lot, was not open source/community oriented, and was not progressing towards being usable. That is why so many of us jumped on Linux because it immediately worked, didn't cost anything, was 32 bit, had a rapid pace of development, and was trying to be usable.
On the Hurd side, there never was anything you could actually download and use. It was also developed very strongly in the cathedral style as many GNU projects were. Of course the promises were that "soon" there would be something. But Linux was there now and accepted patches without copyright assignment, and had rapid releases.