Coming from a somewhat different viewpoint other than as a developer, I spent 10 years working as a full-time reviewer for one of the largest shareware disk vendors, Public Brand Software, and then later for Ziff when they bought PBS. (In fact, my first day at PBS was also the day Ziff took over the company...)

There was a lot of money being made from shareware in the 80s and 90s. I was involved in the Summer Shareware Seminars (later rebranded Shareware Industry Awards) and got to talk to quite a few developers/authors who were making mid-6 figure incomes from shareware, and of course there were a handful that had made their million(s). They were pretty aggressive marketers, though, and not the kind who just wrote a program, distributed it through the BBS ecosystem, and waited to see what would happen.

Disk vendors could make a considerable amount of money, as well. PBS was no Mom-and-Pop affair. Thinking back on it, there were 25-30 full-time employees (office staff, order takers, tech support, reviewers, catalog editors, in-house disk duplicating staff, 20+ line BBS, etc.) I have no idea what type of revenue the company generated, but it was a bustling place!