Well, to be fair, in a pilot you don't generally see a full implementation of whatever is being piloted. If it works on the most vulnerable population, maybe the program will grow.
For example, if you're randomly selecting 100 people the odds of getting someone in the 1% are ~2/3. Making UBI payments to someone in the 1% would likely kill this experiment.
If a ubi program is universal that means the wealthy can’t complain that the poor are the only one being it.