Meowers ...bad code.
I think this is the problem more than anything. I can run games that look just as good or better and with more things going on simultaneously, and I have minimal slowdown if any. In EDO I have near constant slowdown. The space dust causes me slowdowns and I'm not even running the game on a potato. Horizons only had slowdowns in a few select moments. I guess they forgot all the coding tricks from the 16-bit and 32-bit era of gaming to make more with less.