Job pressure
I am sure they are under pressure - they can't be too badly paid - the lads up in Kenya were on huge allowances !!. I guess if Zimbabwe's Generals can rig the results of a an election, then the outcome of a C of A inspection can't be too hard to bend.
The answer is for the EU authorities to ramp check all Zim aircraft after every arrival (for stowaways frozen to the gear if nothing else). That puts the pressure back on Zim. As nobody but Martinniair (I think) go to Zim anymore the reciprocal revenge ramp checks are no longer an issue !!.