That's most likely the technical reason. Once you start adding additional constraints to teammaking (ensure each of the ten players' Elo are matched, ensure both teams have a similar amount of prepartied players) matching up becomes exponentially longer (on top of the exponential hit it already takes simply by virtue of being 10-way multiplayer). This in turn causes players to queue up, get disappointed when they don't get a match within 10 minutes, then quit, exacerbating the problem. If the choice is between having a relatively unbalanced match with a 2 minute queue time, and a more balanced one with a half an hour or worse queue time, most reasonable devs will go for the former.
It's also quite possible that the matching algorithm was created when Smite's population was considerably smaller and therefore a more perfect fit was simply unfeasible with so few players. Still, if the population was so large to support a more robust matchmaking, then the less perfect version would find matches instantaneously every time, not minutes.
Source: Is a software engineer with almost twenty years under his belt and quite a few algorithms, although no matchmaking ones.
That fucking sucks