I'm no Economy expert but I think that when we are talking about a bubble burst,
we are talking about the lost of value. Money is not lost or spend, it doesn't dissapear, money lost its value because prizes increase at a quick [fast] rate. You may have the same amount of money but you can buy less things because you can not afford some prizes.
So, I partially agree with @Jason Bassford
goes fast = the money will quickly disappear (be spent)
but this context is a bit more complex.
According to Oxford Dictionary
Used to refer to a significant, usually rapid, increase in asset
prices that is soon followed by a collapse in prices and typically
arises from speculation or enthusiasm rather than intrinsic increases
From Cambridge Dictionary
burst someone's bubble
to say or do something that shows someone that their beliefs are
false, or that what they want to happen will not happen