I think you are confusing trackers with the more general capabilities that appeared in PC sound cards of the 90s.
Although there were sound cards that supported connecting external MIDI instruments, and there were sound cards that implemented the so-called General MIDI set of instrument sounds on the card itself, tracker software did not use any of this functionality. Trackers loaded samples into memory and mixed the audio in software. This is how Scream Tracker (for example) could output directly to the PC speaker and did not require any particular sound card.
Because everything was mixed in software, the complexity of a composition was limited by the CPU and memory of the computer itself. It didn't matter what sound card you had. On under-powered PCs, loading very large samples or going above 4 or 8 channels of polyphony was not a viable option. This meant that tracker musicians operated under similar restrictions to the chip musicians of the 8-bit era. In fact, quite a few tracker musicians got their start in the 8-bit era, which is why a lot of demoscene music sounds similar to it.
(Edit to add: in case it's not clear, later trackers did use hardware mixing and effects if they were available, but I'm trying to explain more about the culture of the scene and how it influenced the type of music that came out of it.)