I won't speculate about numbers, but until I dealt with people with "spending problems", I had NO IDEA seemingly smart people could be like that!
Simplest way to describe it is that their definition of "I can afford X" is "right now I have more money than X costs". Really!
These people will of course always be poor, regardless of income, subsidies etc.
How many they are is an empirical question, and I haven't seen any data.
One idea to handle them I like is to pay people daily, instead of monthly/biweekly. In the modern computerized world, that should be simple, and could really help some people.