Saying "these are commercial relationships" (that we should try to stop) is different from saying "people are outright buying specific votes".
The problem is that people are too often looking at this as if it is the latter, when it usually is the former. That doesn't mean it's not a problem, but it means that attempts to try to address the latter will be totally ineffective, and addressing the former is far harder in general, because the "payoff" can be very tangentially related and non-obvious.
E.g. it can be as tangential as "look at me giving money to this cause over here that I know that you like (wink, wink)". No direct exchange needs to happen. No direct benefit needs to be had then and there - just the acknowledgement that party X will be very grateful were you to listen more carefully to what they say (not even one on one with you, but say, in a committee, or even in PR releases) and understands your interests.
Direct bribes are "easy" to stop in comparison. And so they're the wrong focus. The consequence of shifting focus to more indirect influence is that the only viable solutions to stop this kind of influence is to disperse power of politicians more by weakening their individual influence, and to reduce the powers of potential beneficiaries of there decisions inherent in accumulation of capital. You draw the conclusions.
Politicians feelings doesn't come into it - nothing you try to do to stop this by regulating their interactions with business will have any real effect.