there was an attempt at initial coordination around the DP-3T and PEPP-PT working groups to get a single shared protocol, but that fell apart, while at the same time many countries decided to go different ways.
Timing was relevant, plus different countries also have different regulations that make specific implementations possible or not.
In the middle of this Google and Apple announced their contract tracing framework so some switched once more.
This can be seen clearly in the documents that the italian governmental task force submitted when evaluating the various apps: proponents suggested home grown protocols, reusing existing apps, or deferred to PEPP-PT or DP-3T.
Even the Immuni app which won the selection was supposed to use PEPP-PT, but then switched to the Google/Apple CTF.
Would have taken too long to orchestrate a communal effort, plus this pandemic didn't _exactly_ make EU a more cohesive, quite the opposite especially in the beginning
Commercial interests and national ambitions mainly. Some corporations found it much easier to sell to specific EU countries than to lobby the EU, so deals were made.
Also, the EU is more keen to protect privacy whereas specific EU member states want (to sell) free reign on their citizens.
This lobbying game plays out all the time. You just cherry-pick your targets, find the weakest link so to speak. In this case, he more authoritarian and neo-liberal the parties in charge of the country/region, the easier you will net them.
