Listening to lobbyists (and implementing the stuff they ask for) can only get a politician money to try and buy votes he can use to cling on to his position. People writing in from his constituency, OTOH, are the voters he needs, and listening to their demands and implementing those has a much higher chance of directly giving him their votes.

Lobbying seems to be more of an issue in central government in the UK, not so much at the local level. But I do agree they have outsize influence.