Soul nights are like records only worth what someone is willing to pay for them. As venues struggle hire charges are being waved making it low risk for the would be promotor. I know of at least one venue that pays the 'promotor' to put the night on in the same way as they may book an act to get customers in.
If people don't value what you put on and would rather see DJ's that are doing it for nothing (presumably playing records that are easy to get hold of) then you can't blame the audience.
There are too few people who value the scene for what it always has been to me; a vibrant scene based on finding and playing new and different music to an appreciative audience. I suspect these people won't be regulars at free events and would rather pay to here good DJ's play quality records but if there isn't enough of these punters to go around you have to be on top of your game, have the right DJ's, with a great sound system, a good dancefloor, in the right venue, in a good location with plenty of parking and still you may not get enough in.
If people won't buy what you have on offer you go out of business. That's a simple fact. In this case not one I like but it is a reality.