This might be something as stupid as export control on cryptography (they use it), and some stupid sanctions control overreaction.
If they cannot control sales of actual equipment through 3rd parties, this way they show how they "try" to comply with export sanctions.
Hundred of thousands of Mercedes cars that ended up on "wrong side of wall" could not be teleported back. But they denied access to support software, spare parts etc.
R&S has major military/intelligence market, and big military/government contracts are what they have been doing as primary market for years. Small business/ private customers are just a supplementary business, nice cream on the top.
If they had some complaints about export control by anybody (or even a hint that might be problem) they will protect their primary market.
R&S is a business.
And it probably makes sense to them.
I personally think it is not going to do anything to actually prevent any proliferation of equipment or any software/FW/manual data where they don't like, but I think they know that too. They do it to show effort was put in and that they try.
So small business/ private customers are going to have to either "beg" for "privilege" to have their equipment maintained properly, or switch to equipment that considers them their "real customer" and respects them properly.
But, don't worry. I expect that soon enough there will be web sites where all the newest R&S FW, manuals and the rest will be re-shared with free access..