It also means they don't make any money if their customers don't make any money. It's a good incentive for providing a quality product, over say, a single lump sum purchase price.
At least, in the start-up phase of operations.
Later, when economies of scale kick in and break-even has been far overcome, one seeks to negotiate smaller unit charges, primarily to capture more of the added value for oneself, and partially to reduce visibility of one’s revenue.
Arguably, once you are a big player in a space, you should ideally have the clout to negotiate a better deal too.
I suspect smaller companies can have the luxury of being more ethically focused if they choose to.