There is zero fraud implied or even suggested by stock buybacks. They are heavily-publicized-in-advance returns of capital to shareholders. That's it. The sales are often offset by the creation of new stock via RSUs, and in that case just reduce the dilution intrinsic to RSUs.
Shareholders want executives to be incentive-aligned to reduce agency problems. Stock based compensation furthers that goal. If a manager doesn't think they have a better use of spare capital than returning it to shareholders, returning the capital is exactly what shareholders want. There's nothing nefarious here.
