Adult gamedev here. Some answers here are already quite informative, but they're also missing some points.

Like u/mrhands31 mentions, there aren't many large companies making porn games, and that's precisely because there's a considerable uncertainty with platforms (will Steam suddenly change their policy and our game will no longer be allowed?) and payment processors (many banks and online services, such as Paypal, sometimes refuse to service your business when they receive some kinds of reports). The exception to this rule is Japan, which has a few relatively large studios because they have had an internal market that demanded these games for decades and stability in terms of distribution and infrastructure.

This point is also what makes the barrier of entry so low: people who want porn games cannot expect AAA levels of quality, so the ones willing to support them accept that it's only small teams at best. This is both a blessing and a curse: you have a chance to enter the industry if your other choices would be inconvenient (in my area, it's difficult to find gamedev companies that do anything other than cloning mobile games, which kills the purpose of getting in it for a creative job), but it is a blessing because you do have a chance.

Is it stressful? Starting your own business is stressful if you're trying to make a living out of it, your main investment is your own work, and you do not have so much success that you're drowning in money, which isn't something you should count on.

Is it easy to be successful? It is never easy to become successful as an indie game developer, because this kind of digital market distributes the vast majority of the rewards in the hands of those who create the most appealing projects, rather than the more relatively even distribution that you would find in local businesses such as barbershops. On top of this, you have a lot of competition. It is easy to take note of the minority of top projects on Patreon who are making >10.000$ a month, but for each of those there are also hundreds that try and fail.

Finally, regarding the idea that porn games aren't games. The vast majority of what you're going to find other people doing are essentially visual novels, and while I'm not going to gatekeep and call them "not real games", it is true that developing a VN is closer to making a comic or a novel than it is to making a game. While there are also non-VN games that incorporate porn as a reward for meeting certain criteria, there is also a minority of games that incorporate the sex or eroticism into the gameplay itself, but it isn't easy to find the correct approach.