Because unless you just don't care about your customers, thinking about the best answer for them is often a good guide. If you don't want to run it anymore, do you think someone else can just pick it up on the fly? FYI, In my experience, that answer is always "No", because SaaS apps are about knowing the problem space, the customer needs, and the history. Being able to read the code is 5% of the work. So people tend to quickly be willing to try, but then get discouraged when they realize the difficulties and just shut down on the customers anyway.
So I'd recommend that if you don't want to run it, but also don't want to just turn it off, find a small group of people who know your niche/market, and who already run a SaaS, and pass it on to them. Often, competitors will turn into partners in such situations. Sometimes that even works best for everyone - you get to escape, your competitors grow a bit, and the customers are taken care of.
That is a lot of rambling, but the overall point is that there are probably more options out there than just sell/quit/keep going.
Also I see some people are throwing their hats in the ring in the comments below, I'd be willing to take a look. My email is on my profile.
Alternatively you can pay someone to rebuild it properly. It could be a fun project for a more junior dev too.
Please reach out if interested and let me know more, let's see if there's a possible deal here. :-)
codewhisperer at team803585.testinator.email (replace the " at ")
Feel free to send me a message, would be interested in acquiring it.
ycom.precut439@passmail.net