Because a lot of them saw that they weren't making as much money as their U.S. middle-man counter parts and wanted a piece of 'American luxury'. Also, by this point, most of the political party had lost the zeal and intellectual rigour that dominated the party in it's first 50 years. It was easier, if you were smart, to either cloister yourself in academia, or become an engineer, than deal with the backroom political bullshit.

We are seeing a similar thing occur in the U.S. where most of the highest political operators are entirely self-motivated, even at the expense of the system itself. There are few George Bushes left in the system.