Yes, it was very much the UK government's decision, due to reciprocity.
There is no question that Germany would have reduced visa requirements for UK citizens, if the UK reduced visa requirements for EU citizens.
During Brexit negotiations, the EU offered UK freedom of movement, similar to how, for example, Switzerland is not a member of the EU but citizens have freedom of movement as if it was a member.
But not unilaterally. One of the duties of the EU is to support basic rights of EU citizens, and one of the mechanisms for doing so is to insist on reciprocity with countries outside the EU. If the UK will not grant EU citizens rights in the UK, then roughly speaking, UK citizens are not granted equivalent rights in the EU.
Naturally the UK turned that down, which closes the border to UK citizens going to the EU, just as much as EU citizens going to the UK.
Weaker, limited forms of freedom of movement were also offered. For example the Erasmus student exchange program, and visas for travelling performers.
All turned down by the UK. Thus the EU institutions and member countries are not minded to offer UK citizens rights, even limited, which the UK declines to offer to EU citizens.
As a Brit who has now lost their ability to work in the EU, and whose children will not have that wonderful opportunity to travel and work in a multitude of countries which all EU citizens enjoy (and many of them use), this is a profound loss.
It is not a surprising outcome, though. Politically, most speeches I heard by Theresa May during the negotiation period started with something like "on XXX date, freedom of movement will end".
The removal of freedom of movement was emphasised as a central, non-negotiable purpose of Brexit during such speeches.
So it is not surprising that it was stripped from us, because that freedom will not be removed in one direction only. And it's not surprising that the new visa requirements are the "hard default" which apply to countries that have declined to negotiate something better. Germany is unlikely to offer UK citizens preferential treatment so long as the UK holds an equivalently hard stance against German citizens.
Recently, I read that children from Germany no longer come to the UK on foreign exchange school trips, even if the purpose is to learn English. They have switched destinations to Ireland, Netherlands and elsewhere. That's because UK visas for such trips are now too difficult and expensive to obtain. Also, about 4% of children in Germany are non-EU citizens, and in practice those would have to stay at home while their classmates travel (before Brexit they could be part of a travelling school group). So the UK foreign exchange school trip industry for EU children has now collapsed, and the UK is no longer a place they'd think of visiting.
With that sort of abrupt change of rights affecting German citizens and residents, and the UK making it clear it doesn't want to make such things easier even for temporary stays, let alone working, of course Germany is not going to offer preferential work visa options to UK citizens.