One of the reasons why UBI appeals to the HN crowd is because the HN audience leans towards entrepreneurs and wannabe entrepreneurs. But for the economy at large, far more people would rather try to keep their heads down and get home to their families.
Most people are not responsible financial stewards. They don't take their excess income and put it into investments, they take their excess income and put it into improving their standard of living. That means using the extra income generated from a day-job goes to higher rent, car payments, and other liabilities not easily released.
Most middle-income people will end up in the same place - unable to leave their jobs due to the difficulty of finding a new one. Upper-income people will pay more in taxes essentially to end financial insecurity among lower-income people living paycheck-to-paycheck.