Most of the time leadership doesn't need to pressure individuals, because they follow the commands -- not because they so well aligned on all topic (they are not).
Of course there's an argument to be made that it would be a lot more chaotic if every elected MP truly was only beholden to their consciousness, because your certainty of how some vote will go would be very low and you'd have to actually convince MPs that it's the right thing to do (that would open up the question of transparency, i.e. who voted for what; official German politics are fundamentally opposed to that idea).
Brokering backroom deals among party elites is far more efficient and predictable -- you can always buy agreement by offering some concessions on a different topic they care about. But then we're back to that question: why do you need hundreds of people if the decisions are made by a few dozens?
Of course there's an argument to be made that it would be a lot more chaotic if every elected MP truly was only beholden to their consciousness, because your certainty of how some vote will go would be very low and you'd have to actually convince MPs that it's the right thing to do (that would open up the question of transparency, i.e. who voted for what; official German politics are fundamentally opposed to that idea).
Brokering backroom deals among party elites is far more efficient and predictable -- you can always buy agreement by offering some concessions on a different topic they care about. But then we're back to that question: why do you need hundreds of people if the decisions are made by a few dozens?