In order to monitor encrypted communication, investigators will in future, according to the Senate draft and the Änderungen der Abgeordneten, not only be allowed to hack IT systems but also to secretly enter suspects’ apartments.
If remote installation of the spyware is technically not possible, paragraph 26 explicitly allows investigators to “secretly enter and search premises” in order to gain access to IT systems. In fact, Berlin is thus legalizing – as Mecklenburg-Western Pomerania did before – state intrusion into private apartments in order to physically install Trojans, for example via USB stick.
You’re right, they probably wouldn’t bother for the vast majority of people. Also, for the typical computer that isn’t security hardened and is also connected to the Internet, you could do the entire attack with a few seconds of access.
This kind of attack is referred to as an evil maid attack, if you want to research tools and methods.
If they’re trying to uncover a conspiracy of multiple targets, being able to bug the electronic devices of any of the members will give them a lot of ongoing intelligence and opportunities to infect additional target. Being able to image a device before the target is aware of the investigation (who then alters/deletes the data) is also important in a lot of cases.