The answer is you don't sell the tool. You release the tool, others help you make it better, then you use the tool to build the actual thing.
It's not just FOSS: the era of commercial software is equally over. Why pay for something that leaves you dependent on a third party for bug fixes or new features? Vibe it up yourself, and pay for only what you need, when you need it.
Dev tools are a tougher sell because other devs can make them. Your normie SP500 manager isn't going to whip up some project management software in his free time.
The successful business model is more like make tool, give away tool, make random project management/accounting/tool that devs would never use and normies can't make.