Edit: I submitted Cov19Tech as a Show HN earlier today: https://news.ycombinator.com/item?id=23395475
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.
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.