Politicians are real people with families to support and the fact that large companies are prepared to offer jobs and pay them well suggests they think if they can function in the mad house that is Parliament that they can deal with anything. Some are recruited for their contacts, but nowadays anyone working for a big company at a senior level is expected to bring more to the job than contacts.
I can think of no good reason why ex politicians should have to be more noble and self sacrificing in their choice of jobs than anyone else. An awful lot of people work for Facebook, Amazon, M&S, etc etc. Why should politicians not work for them. They are meant to be men and women of the people.
The significant thing is that no one has offered David Cameron a job and it will be interesting to see what happens to Teresa May if she chooses to leave Parliament, although as she is in her early 60s and will almost certainly see this Parliament out, she could always opt for early retirement.