I don't even think it was a cash-in. It was...just...bad. Really, sonic 06 was so incredibly bad, across the entire spectrum, that if Sonic Team had actually held a meeting and decided to make "the worst sonic game ever", it wouldn't have been as shitty as Sonic 06 was.
The things that made Sonic 06 bad were deep rooting, and I think so lowly of Sonic Team as of late, that I honestly doubt they could make it that bad on purpose if they tried. They'd probably fuck that up too, and it'd be the best sonic game ever.