They are nowhere near stupid.
They don't want to reliably deny Russian citizens access to some specific sites (why would a sane government ever want that?).
They want to be able to quickly suppress any protest rally on the internet when the hour comes (if it comes at all). To achieve that, they don't need to patch all the holes; it's enough to know where holes are. Should the hour come, all sites used for hosting protestant communication will be shut down "due to technical reasons" (if not completely legally by that time - new legislation is being passed all the time) and all proxy IPs will be banned on ISP level.
This means that one needs to block sites which few technically savvy people need badly, but which are not crucial to the general public. Such tactic reveals proxy/vpn endpoints and other evasion methods without causing an uproar. Which they did twice to github (re-allowing it back both times), and which they seem to be doing to linkedin now.