Are you thinking of any specific one out of the "so many" examples, or are you assuming? Because for Senators, it's illegal to sit on a corporate board, and for Members of Congress, it's only legal if the position is unpaid: https://politics.stackexchange.com/questions/10976/legislati....
However their relatives can sit on boards, so a senator's spouse would be fair game. And they can use the paid board gig to make money between terms.
Susan Bayh, ex senator and governor from and Indiana married to another senator, sat on multiple boards between her own political terms and while her husband was in office (also while she was governor). She's been on at least 14 boards in total: https://en.wikipedia.org/wiki/Susan_Bayh
Are you suggesting that spouses of Congressmen shouldn't be permitted to sit on corporate boards? (And presumably, should be excluded from any of a range of careers in the private sector.)
No, I'm just claiming policy makers can be influenced by corporate boardrooms. I don't really have a solution for it, and I can't really say that I know whether or not this is a big problem that needs solving, but is there legal ways for companies to use board positions to affect policy makers? Yes.
Personally, I don't think it's the worst. I would rather they had to do this than get huge retirement packages as they do in my country after their service. Also, if their spouses can make a living being involved in business so politicians can't use sympathy for their poor family as leverage to get higher compensation that would be good too. But we can't handwave the issue of corporate influence over politicians however we choose to deal with this.
They can get around that through the "revolving door" between legislators and lobbying groups: opensecrets.org/revolving/
The old "you pass legislation that we want, and we'll have a seat waiting for you on the board after your term is over, with a nice paycheck attached".