Yeah, coding in jungling for bots would be a lot of trial and error, but Riot has plenty of professionals whose job is for doing this sort of stuff, surely it couldn't be that hard for them?
I have a master's in Computer Science, and that shit is hard. Like, "if you successfully did something like this it would be considered a huge step forward in the field of AI" hard. Riot has said they've taken a few stabs at it, and the bots just end up feeding even harder than the laning-only ones against good players.
Doom Bots were hardcoded to go to the dragon/baron pit every time it spawned. In fact, IIRC they teleported there. Real people can't consistently make good calls about when to contest Dragon/Baron, and you think Riot can make AI that does it better?
Now, you could have cheating AI (moreso than it already does -- like it could always have vision of everyone, even more free items/gold, reduced cooldowns, etc.) to make it harder, but I'm not sure this would really improve the feeling of the games.