> Why is that?

Well, if I'm very motivated, I might write a letter to my MP once or twice in my life. I could do more, but I simply have other stuff to do with my life, including my own work.

A corporation, on the other hand, may hire people to pester my MP eight hours a day. These people may have enough money to treat my MP to a lunch, etc. And when my MP stops being elected, that corporation may offer them a job.

Why isn't really an enigma here.