What is the problem with candidates taking money from millionaires/billionaires?

Everyone, no matter who you are or how much money you make, can only donate $2,800, as an individual. Here are the other maximums. What makes anyone think that because Bill Gates, for instance, donates $2800 to a certain candidate, that said candidate is thus beholden to him.?

There are also charts like these that indicate how much employees from a certain industry gave to the Democratic candidates. This would include donation from a CEO all the way down to a tech nurse, but no more than $2,800.

Most, if not all, Democratic candidates do not take PAC money, and many have agreed to not take any money from certain industries, like fossil fuels.

So what is the problem? Just because Bill Gates donates $2,800 to Klobuchar does not mean that she is going to do his bidding. I paid a decent sum of money to meet, greet, and eat with a candidate and I was not promised an ambassadorship or given a promise about addressing my individual concerns.

What am I not understanding?