^ many Thai restaurants seem to use those tiny pink tissues, which if used singly aren't enough to do anything. You end up having to grab several of them just to clean up. When they're packed too tight, they do tend to come out in a wad, which usually is more than you need. So you're left with either leaving the extras on the table, in which case they may be thrown away and wasted. Or, you can pocket them or try to stuff them back in the holder.
In the long run, it would probably be cheaper for the restaurant to provide napkins of sufficient size to be able to use just one, but the ability to determine that seems to be lost with the mindset here of cheaper is better. The proprietors are probably also worried that if they put more expensive tissues out, they'll be more likely to be pocketed.