I purchased a copy of OSF Motif for Linux (x86) sometime in the early 1990's (before it was free). I had used it before on SunOS and I liked it.
One of the most annoying things about it was that it did not address the endianness of the arguments to the library functions. So it worked fine on big endian platforms, but not so fine on little endian ones (such as Intel).
It would still work okay if you byte swapped the arguments in and out of the library functions, but it just seemed silly to need to do that, and it made it more difficult to write portable code.