They're not going up the path, but instead, they're piling up at the bottom of it.
It's really easy to kill them.
Viewing post in Hopping on robots
Ah, now I know what you mean. Yes, they're a bit daft when it comes to getting back up the ramp. This is balanced out by Spidertron in the later tiers, but I agree it's pretty easy to lead them around for some quick kills. - I'm not quite sure if it's a bug, but I'll make a file for the AI. Thanks for the report!
-Cheers