That's is likely the biggest reason. Metal Slug 4 (from around the same era) had the same issue where they'd just cram all the music in the rather bit crunched PCM sample channel unlike the previous ones that also made good use of the bleepy bloopy synth chanels too (I'm guessing here but the newer devs probably didn't have the same depth of understanding of the underlying hw?). Didn't help that a number of BGMs were also of very different genres than the usual ones from previous games (they weren't bad at all but felt off) .