Why they didn't take the FAA system lock stock and Barrel and adjust it to suit EU requirements God knows. It would have saved 100s of millions of EU money and a lot of aviation a mass of headaches. it would also have lead to an international standardisation of regulations and hence safety in aviation
But no that was too simple too cost effective and too pro aviation for the EU
Because in that case the paper-shufflers and such would have had a hard time to justify their jobs and relative paychecks.
Many public agencies don't serve the community but just themselves.
On top of that, if a guy already has an FAA license with all ratings perfectly valid in Easa-land, no FTO will be able to make much money out of him.
No validation, no checks, no FEES.
Not good for local business and local CAA.