Riot has said they've prototyped jungling bots and they just feed horribly. Real human players can't consistently figure out good times to take Dragon/Baron and you think Riot can slap together some AI that would do better?
It would take a massive overhaul of the AI system to have a chance -- it would have to actually "understand" (to some extent) global pressure and vision control, and be sneaky and unpredictable enough to gank real players without constantly walking right into counter-ganks. It would be a huge project for something that would likely have niche appeal among their playerbase, and I'm sure it would require a lot more server-side CPU time to run such bots even if they could make it work.
Doom Bots took dragon, but they were hardcoded to just teleport there and nuke it down. They didn't really have any intelligence about it, it was just hardcoded (and they cheated and teleported there rather than actually setting up roaming opportunities, warding, etc.)