Why do short stacks push and then rebuy.

[Percula]

I am sure anyone that has played live has seen this (happens online too, but much less often). Doesn't really matter if it is LHE, NL or PL. They buy-in for a normal amount say a rack of the color of the table, they play, get sucked out on, play badly, make questionable calls, etc.

Now they are down to just enough to play another hand and the next thing you know they are AI on the flop or turn with a very questionable hand, i.e. one that is very likely to not win. Lose and rebuy for another rack. They have enough in their poket to rebuy multiple times, but they only buy in for a minimum, bust and rebuy again and again.

So is the mental process here? What are these people thinking? What is their motivation?