Because elected reps believe that they need to support constituent businesses in addition to constituent people. And those constituent businesses spend more money to ensure they are heard.
I have often wondered if we could split the house in two: one for people and one for industries. This would force transparency and bring the primary issue of double speak and lobbying to the forefront. It would turn them into official cogs in our body politik instead of forcing reps to work and speak in a duality.
Do you expect voters to switch sides of the aisle over this issue? If not, then politicians have no reason not to take industry money. After all, if you have access to all the campaign and other funds without losing voters, then it would be idiotic not to follow the money.
Because we are effective parents and do our job, they don't get their way.
I can't see why our elected representatives can't manage to act with the same level of responsibility.