I think you vastly under estimate peoples will to advance. Would some take easy or no jobs sure, but not everyone wants to get by with a fixed income. They will always want to buy something UBI doesn't enable them to buy.
A nice vacation, nicer larger home, new car etc. UBI would just give people the cushion to take a risk and know if I fail I don't end up homeless. Or the piece of mind to relax and know they can eat a healthy meal and pay rent no need to work 2 or 3 jobs. Maybe the reinvest in their education.
Clear misunderstanding of incentives. Most people would chill or take easy fun jobs.