The word from the Ben Hurst interview I saw was simply that there was new management coming in to ABC. They wanted to make a mark and SatAM just wasn't on the list of priorities. Who really knows though?
Ah. I wonder if there will be another show.. After Sonic X (not that it was horrible), I don't expect much, but it would be interesting to see what's next. Actually, I remember hearing something about a Sonic Underground reboot, but I think it was fan-made or just fake.