Simply because all the niche's for software are getting filled. Leaving only opportunities with huge hurdles to get over, which is hard for one man companies.
In the early days micro isv's were fairly common, and well known. I don't hear much about them anymore.
>Simply because all the niche's for software are getting filled
There's also a ton of new niches opening up, but you need to be aware of them and they don't happen in a vacuum. You can't just sit in your home office that imagine a new niche, you need to surround yourself with people doing other stuff.
Even if you surround yourself don't expect to actually understand. Lots of niches, probably most of them, require expert knowledge of the domain that's not easily acquired unless you are actually working in the niche and dealing with that stuff hands-on. The alternative is if someone with expert tells you their problems and then actually help you understand their domain, because they are willing to do that for you. But it's often not easy finding people that will actually help you acquire enough domain knowledge to be able to implement the solution to a problem.
In the early days micro isv's were fairly common, and well known. I don't hear much about them anymore.