MaRo did an entire podcast about tribal
here. Basically, the next logical point to use tribal after Rise of the Eldrazi would have been Innistrad, which had a heavy tribal component, and indeed, design had several tribal cards. The problem was, it was only ever relevant for effects like "return a Zombie card from your graveyard to your hand", but otherwise, there was just inexplicably this extra set of words on the type line that didn't affect gameplay at all. It wasn't pulling its weight in Innistrad, so they removed it. It appears that Innistrad is as heavy with tribes as Wizards ever wants to get, after they concluded that Lorwyn was too heavy with tribes, and if tribal cards couldn't work there, there was no point in using them at all anymore.