Paint will still bleed if left long enough. It’s just layers of cheap polyester and even cheaper carpet padding sewn in a quilted pattern. There’s a reason they are cheap.
Actual leak proof drop clothes are made of marine grade canvas, have a rubberized bottom layer for grip/leakage, or are treated with some type of coating to make them waterproof and flexible.
Ok, drop some lacquer/toluene based paint on your rubberized canvas and it will also leak. There is no material which is perfectly leak proof with all solvents. Go a head and spend hundreds of dollars on one of your rubberized marine canvas drop cloths, it ain't coming out of my wallet.
If your painting in your home, these moving blankets are at least 3x thicker then the best big box store heavy fabric drop cloths, likely 5x cheaper. Yes you are correct, If you spill a gallon of interior paint on them it will get through the material in time, but not your common paint droppings.
As moving blanket, they are a very good buy at 65lb weight, nothing like the horror freight blankets . Again I am sure you will find better moving blankets at a ridiculous cost, but again it is your wallet, not mine.