In a construction company, just because everyone is carrying tools that would let them break into the Dynamite Storage locker doesn't mean that you should just give everyone the key (or not bother to lock it in the first place)
Similarly, just because it's possible for a knowledgable person to bypass the restrictions on installing software on a machine doesn't mean that yhere are no cases where such restrictions make sense.
As far as I'm concerned, per-user application installs really don't make much sense nowdays. Almost all systems are single-user, so there is only the one user to install the app for. The few cases that remain where there are multiple users on a single system image are all cases where it's probably a bad thing to have users installing software (especially given how easy it is to have separate system images with either virtual machines ot containers to isolate the users when you do want them to share hardware)