>>714210938 (OP)Because it lost the core aesthetics the OG game had. It became cleaner, brighter and, for the lack of the better word, more "fantastical" than the original game was.
It is honestly best exemplified by comparing the look of the protoss and the zerg in SC1 to their SC2 counterparts. They became just far more cartoony and less down to earth/realistic/grimy.
Terrans suffered slightly less of this aesthetic devolution but they too became more cartoony just not to the extent as the other races did.
The storytelling also became just worse in general.