Boss Rush was an anonymous blog, currently deleted, run by someone who actually turned out to be Sonic Europe employee Ben Andac (who is no longer with the company). Among other things, he clearly knew about the impending "Werehog" gimmick of Sonic Unleashed a full year before the game's trademark was even registered. On the subject of Sonic the Hedgehog games, Andac had this to say, as preserved by archive.org:
Instead of using the re-structuring for good Sonic Team became complacent slaves of their earlier successes. Their primary goal now is purely business driven: to please the managing directors wth good ROIs; this is not so abnormal - it is a business after all - but they leave little room for creativity and originality in their particular brand of working practices.
... Clearly the blame does not lay squarely at Naka and Sonic Team's door - the direction of Sega (or rather Sammy) as a corporation; the narrow-minded short-term annual business-plan practices and development processes (i.e. tight development schedule) that demand yearly churning out of Sonic products all play a major part...
So that's why Sonic is constantly in roughly three or four games a year, despite few of them being any good. To Sega, the Sonic franchise is now a money train the company is willing to ride all the way to shovelware station. As long as gamers keep buying lousy games starring Sonic, nothing is going to change.