Yes it is rife, and yes it probably does happen in 90% of transfers, but the FA can't do anything without proof of it happening.
So in the majority of transfers, it's the agents talking to clubs rather than players, which makes it very hard to prove anything is happening at all. An agent is hardly going to do himself out of a job by talking about it.
In VVD's case, and I say the following without obviously knowing any details, but it appears that there is proof of Klopp talking to VVD, text messages and so on.
So the FA have to act if the complaint is made and there is proof. You have to see the difference?
What you seem to be arguing I akin to saying the DPP shouldn't pursue any murder charges ever because other murders are unsolved.