Originally Posted by
PizzaSHARK
Because it's better they learn what the heroes do there instead of joining a game with players and effectively ruining one team's chances of winning.
Bots harass effectively, are somewhat competent at last hitting (don't think I saw them ever deny), and usually are pretty good about ganking and grouping together. They'll teach rank newbies everything they need to know in order to do something other than feed, rage about OP, and abandon when they start playing vs players.
Honestly, they should really just force everyone to play (and win) at least 10 botmatches before they're allowed to queue to play against other players.