Sometimes it is not greed though but also a fear to lose more.
It is most likely the fear of losing more. Some people may see it as greedy because the player keeps tossing in more. But for some who have been and experienced the same thing, they know the player is trying to gain back what he/she lost.
Betting more could signify both things but the real thing cant be determined because we don't know on whats that player do had in mind its neither being greedy or chasing up his losses.