Each software development company gets income in different ways. There are companies that develop software for each client individually and their income is the calculated development cost, which includes a large number of factors: the complexity of the project, what specialists were involved, the number of work hours, whether freelance specialists were involved or not, etc. There are companies that develop "tight" specialized software, for example, PMS software for the hospitality industry - https://www.bookingninjas.com/, and sell it at a certain cost to the relevant companies that need it. The option of monthly, annual, or some other subscription can also be used. In addition, many companies add advertisements to their applications (especially often seen in applications for mobile phones). Therefore, this issue is quite complex and extensive. It all depends on many factors.