It sells the most, so from a marketing standpoint it makes perfect sense.
Considering the quality though, I do think it is embarassing. Sonic in the last 10 years has given SEGA a childish image they have never had, so it brings down their other franchises. Excess Sonic focus has also created 'Sonic fans' who do not even like SEGA, which seems bizarre. Mario fans like Nintendo, for comparison. Considering that, they probably are Nintendo fans who just associated Sonic with Game Cube, Wii, GBA, and DS.
So to be blunt: yes, they should stop, it brings in irritating people.
Alternatively they could drop the last 10 years of garbage and focus on quality, but I do not expect that.