Simply put, Tendril combo make red and green deck mostly unplayable. Playing a deck that has a 0% matchup against combo is silly. And i don't think that's the fault of the colors design, i think it's a fault of the storm mechanic, it's not a "combo" , much more a "uncounterable burn.dec".

Dragon is countered by much more card than Storm, the same goes for Belcher, Ichorid, Cephalid, Life, Hermit Druid.dec, etc etc (a lot of those are countered or hosed by fanatic, go go red!). The simple fact that those deck wouldn't be played in the presence of storm, and that many of those deck have their core card banned, it's a clear indicator on how much Storm isn't good for the format or either the banned list is terribly outdated.

p.s. And please don't put CotV in the list of "splashable hate". It may seems splashable because it's colorless but it really isn't.