Red Hat, for example, immediately
went after the Corporate market, where support is basically a required part of the bargain. You pay
for RHL, but you get excellent support and updates as part of what you paid for. They have also engineered things to reduce maintenance and upkeep costs for corporations, who might be running many hundreds of RHL servers. So, they were a stock that I bought at their IPO ...
... because I knew they had read their market well and had a sound, sure to be revenue-producing financial model. Which they did.
And, even when a "distro" has a paid option, I generally pay for it. I don't mind doing my tiny part to keep their lights on.