I suspect that there are a lot of factors.
One is that there are a lot of universities in the US that have masters programs, but no doctoral program. Some of their masters students just continue on from a bachelors at the same place.
A second factor is that there are more needs out there for education and "mad skilz" than you might expect. Programs in management, for example, are often taken by employed (night school masters) for advancement in their current job. Employers used to pay for this, but I think that is rare now. But an advance will come with better salary and more opportunities. I've seen the same to be true among software developers. They want to modernize their skills, but not do research. The masters may be tailored for these needs where doctoral study is not.
A third factor involves what a student's advisor will support. Some will recognize that a student isn't really suitable for a career in academia and will only write letters for masters level applications.
A fourth (probably minor) factor is that not all students understand that you don't need to get a masters first to join a doctoral program in the US and, perhaps surprisingly, no one tells them otherwise.
A fifth factor is that some people just have different goals than others and, while they want to learn more, don't really consider doctoral study and/or don't want to game the system in the way you suggest they can.
A sixth factor, of course, is that the standards and requirements for admission to doctoral study are pretty high and the competition is pretty fierce. Someone faking it will probably give of "tells" that can be caught during the process. If you don't express true commitment in you SoP then you are probably less likely get in.