Designer, developer, and other salaries is one big thing
You’ve got project managers, devs, user experience designers, possibly legal counsel, testing engineers, and others that need to get paid. A quick google search of the average software dev salary in the US is ~120k/year. Depending on what all the app does, it could easily take months to a year to go from an idea to a public release ready application. That’s a good chunk of people needing to get paid.
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