Answering the "why do you want to do a PhD?" question
Let's consider why "you are telling [professors that] they shouldn't admit you!":
- I felt I'm in a dead-end job...
That doesn't show motivation for doing a PhD.
- I wanted to swap careers...
You don't need a PhD to swap careers.
- I choose this field because...
...it provides transferable skills to the careers I want to move to...
This requires more detail to be relevant.
...because I'm sufficiently interested in it to want to keep up to date with its most recent developments...
You can do that without a PhD
...(even though I probably won't stay in it as a researcher, per the fact that the odds of finding an academic job are very low).
This doesn't show motivation for doing a PhD.
- I did well in my Masters (which was in the same field)...
Many "do well" in their Masters, PhD students do better.
...including the research component, so I believe I can also do well in a PhD.
This requires more detail to be relevant.
- I can afford it.
This doesn't distinguish you.
Performing a PhD thesis can be tough at times; there are times when your experiments do not deliver the results you want, when your articles are being rejected (sometimes with unjustified criticism, or at least it appears so to you), when you are working long hours, when you are suffering from writers block, when you have to teach unmotivated students, etc etc etc.
https://www.google.com/search?q=PhD+blues
Not all of the above may happen to you, but some of it may occur at times. And in certain fields and geographies you are absolutely right about the economics; a career in industry may pay more than in academia.
So when asked the question "why do you want to do a PhD?", people are looking for your motivation. They would like to see candidates who are intrinsically motivated, who like doing research, who like to publish, who like to contribute to academic knowledge. Because these kind of people are most likely to overcome the hurdles described above.
If a school is acting morally, then it takes pains not to admit students who are unlikely to succeed. So we give the SAT to high school students and hope the score predicts whether they are apt to graduate college. (I know of a school which lost it's state funding because they admitted too many ill-prepared freshmen and over 50% of the freshman class dropped out that year. It appeared on the surface that the school simply let them in, took their government financial aid, and let them fail. IMO, this was fraud. Also in the state's opinion.)
So how to we decide if a person will be a successful Ph.D. student? We want someone who is enthusiastic about the subject and someone who will contribute to the on-going mission of the department. I think most of us believe that the type of student we're looking for will be internally motivated. All of your reasons are external motivations. We'd like to know that the reason you're with us is because the craving for this type of knowledge is part of YOU, not part of the circumstances you happen to find yourself in at the moment. Internal motivation is more permanent and more stable. Your external motivations can change at any moment. If you win the lottery, will you immediately drop out of the program and leave a pile of dirty test tubes for someone else to clean up?
I look at your first 3 reasons and think, "The instant this guy gets an offer he likes, he's gone. He's a mercenary."