One problem is that so many of our politicians now choose politics as a career straight from university. they work as interns, then they get jobs in lobbying group, political PR, think tanks, party HQs and the like while angling for parliamentary seats.
Once in parliament, their only aim is to stay there and get their pension, it makes them malleable and biddable and always prepared to compromise their principles for party promotion because they know if they get kicked out of parliament they are unemployable, unless they can get back on the party merrygoround again.
In the past most MPs had had other jobs, had skills and professions they could return to, or private incomes, that meant they were not slavishly devoted to toeing the party line. Now we are dependent on those with private incomes for indpendence of thought and action in parliament - and that is not a good thing.