What is the reason for not providing glide slope guidance on the western approach to Innsbruck?
Looking at the charts, I can see quite a few good reasons for not providing glideslope for the West approach:


The East approach leads you (almost) directly to the runway threshold, the West approach leads you a few miles east of the airport.
The East approach has more terrain clearance. If you go only slightly below the glideslope for the West approach, you will be dangerously close to terrain.
The descent profile is steeper for the West approach: you are expected to lose 1500 feet for every 3 miles you travel. For the East approach it's 1320 feet for every 3 miles.


Number 1 is very important. If some pilot decides to blindly follow the ILS needle on a East approach, eventually he'll see the runway. If a pilot does the same on a West approach, eventually he'll crash his plane somewhere in the valley. The absence of glideslope reminds the pilot he has to pay attention to the vertical space.

Tracking the glideslope accurately is also pointless, as the pilot will transition to a visual approach and circle around anyway. It won't make big difference if you were a little bit off the initial descent.



For reference, East approach:


West approach: