If you come from a wealthy privileged background and your full-time job is making independent movies or off-off Broadway productions YOU CAN AFFORD TO PAY THE ACTORS.
But exploiters will NEVER run out of reasons why they MUST exploit actors. The best excuse of all time was offered by Edward Einhorn the douchebag who registered an unauthorized derivative copyright based on my play TAM LIN and then used the illegitimate copyright as the basis of a lawsuit against me:
Well, I think the theory behind it all is that the actors get the glory of having being on stage, which is why they are usually happy to work for free...
Get that - actors are USUALLY HAPPY to work for free. Not, actors endure working for free. Not actors are actually subsidizing the work of douchebag men who mistakenly believe they have anything of interest to say about anything. "USUALLY HAPPY TO WORK FOR FREE."
Meanwhile most of the actors that I know - which would be the ones exploited by the likes of Edward Einhorn - are barely getting by. Most of them don't have a trust fund or a wealthy family to fall back on.