In this case why the width of the runway strip is not 137m+137m=274m?
I don't know - you'd need to ask one of the team who wrote that bit of Annex 14.
But I'll hazard a guess - no guarantee that I'm right though!
I think the problem is that you're comparing apples with oranges. The strip is there for the reasons that you cite. The location of the holding point is (usually) put where it is to protect the ILS signal.
I would imagine that the dimensions of the strip for each code of runway is based on a collision probability model for where an aircraft using the runway might end up if things go pear shaped (which is how many, if not all airborne separation standards are derived). I would expect that part of the model will consider the probability that an aircraft - of the the maximum size able to use the runway - will be at a holding point when another aircraft is using the runway, which often is going to be surprisingly small. This is all part of risk management - and as we all know, if you want aviation to be absolutely safe you have to stop the aeroplanes flying - but, the probability of a collision between one aircraft using the runway and another at a holding point is considered to be 'safe enough' using the strip dimensions in Annex 14. And experience would appear to bear this out.
Therefore - if you consider a holding point for a code 4E runway where the holding point does not lie within the ILS sensitive areas I would expect that holding point to be 60m from the centreline.
If the holding point somewhere is near an ILS sensitive area it will have to be located at the the sensitive area boundary which will probably put it further from the runway.
Imagine for one moment an ILS with a runway/taxiway configuration such that the aeroplanes are nowhere near a sensitive area at any point and the holding point location would be determined by the strip width only. Of course this is not going to be possible with an ILS but some of the 'new' precision approach systems don't have ground-based equipment or have a ground element that is not so sensitive to disruption. So a runway with a GPS-based approach could have holding points closer to the runway than one served by an ILS. In fact, better runway utilisation because aircraft will be able to line up more quickly is one of the operational benefits expected at high density airports if/when they move to GPS-based approaches.
Hope this makes sense! It's years since I dealt with this sort of stuff so my apologies for any inaccuracies (which will down to me) but I think the principle I've described is correct.