To get that data, governments may need a bunch of things: the company being under their jurisdiction in some legally relevant sense, laws allowing for such requests (those may or may not be needed, sadly), the company keeping the data. If the company doesn't keep the data, they could try to compel it to or hack it, but those may be more difficult. So that's a lot of steps.

For this reason Signal is hardly comparable to Whatsapp and many other apps using the same protocol: the latter group openly logs metadata, the former says they almost don't, is open source, is more trustworthy due to the organizational structure. Finally, there's even some evidence ( https://whispersystems.org/bigbrother/eastern-virginia-grand... ) that they don't.