Perhaps the division of revenue needs to be communicated more clearly to new instructors. The communication needs to be simple and clear. Let me give it a try.
In every business there are three major components of the process that delivers goods or services to a customer. One is the creative process (R&D, design, engineering), the producing process (the computers, software, the factory), and the sales/marketing process. The instructor creates the product and we rely on Udemy for the producing and selling of our product. Udemy is primarily a marketing company and that relieves us instructors of that so we can focus on the creative process. The revenue paid by customers is divided between these three functions. Instructors receive 34% of the revenue (37% minus the 3% transaction fee).
While some other platforms offer a higher percentage they do not match Udemy in marketing. We trade some percent for a much more competent and robust marketing operation that results in revenue for instructors.
(OK, that's my attempt at a simple explanation. There are long debates about this in other discussions, please lets not repeat them here. But, if someone can offer a better, and simple explanation, let's hear it.)