It's a matter of political philosophy and historical context. Back then, before we had TV, the internet or even the radio, communities were more tightly knit and your world was your community. You elected your MP to represent you and didn't care how they did it.

Nowadays, people's horizons have expanded and their community is the world, so people don't vote for their MP, but for the party and/or prime minister. Therefore, our Westminster system is no longer aligned with its original goal of representing its constituents above all else.