A septic system isn’t that expensive nor hard to maintain.

OPs scenario is paraphrased as "shack out in the woods removed from civilization". Getting the equipment and workers out to such a place would present the first challenge.

If you have access to well water you can run it near independently. Assuming electricity of course, which is often available even in places without sewer or water.

See, now we've raised the bar to not only requiring a sewage solution, but also dependable electricity and water source. This is why a functioning society is so valuable. It can provide easy and cheap access to dependable water, sewage, electricity, and skilled workers to build, install, and maintain the systems that let the toilet function without a second though.

All you need is to occasionally pay someone to come and pump the tank

See point #1.