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.
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.