Some of them think they can have several jobs and treat being a MP as a second job. One lawyer MP was based in the West Indies for while because he was in court over there. He said he earned more as a lawyer than as a MP.
They like the status of being a MP and particularly Minister, it strokes the ego of some.
A venture capital manager may earn more, but they are fairly invisiible and are not seen to control the Country.
Maybe we should question our MPs at election time about how many jobs they have and plan to have.