And who do you think are members of those standards boards/committees? Employees of corporations!

Influence is not always overt or malicious, but it happens. For example, a corp wants a new feature in C++ stdlib. They hire someone (or get an existing employee) to build the new feature, submit for adoption to the standards committee, present at conferences, handle RFC feedbacks, etc. until finally the feature is accepted.

It's exactly how the process is intended to work.

In reality, usually they just release their own implementation with non-standard features and popularize them, resulting in either compiler lock-in or de-facto adoption in the standards as other compilers adopt them as well.