There are a number of factors that differ from a musician sitting down in a social place and performing with hat out (and often needing friend to circulate out in the crowd to request payment.) There’s the social pressure of others watching you, there’s seeing other people pay, etc. These don’t necessarily exist on the net which will probably result in little or no payment for the street musician on a site. Which is the current result for many contribution buttons.

The issue of sustaining through payment ones work on the net is a vital one. And it needs to be looked at in depth.