Fasttracker II was a 32-bit DOS executable, but trackers in general (and the MOD/XM formats) were born [1] during 16-bit Commodore Amiga era.
The Motorola 68000 was a 32-bit processor. What Commodore Amiga was 16 bits?
... but not entirely. The registers were 32-bit but the ALU and data bus were 16-bit.
The 68020 was the first 68k chip that was 32-bit without having to qualify exceptions for different parts of the architecture.
The CPU was 32-bit but the earlier Amigas (A1000, A500) and STs had 16-bit data buses. That was probably why.