I'm afraid I have to disagree about lack of training.
I'm currently involved with teaching Lineys at a front line base and evey time it comes to teaching how to do oils we repeatedly stress TO READ WHAT IT SAYS ON THE TIN.
I don't think you can necissarily tie it down to a single cause. A combination of habit and complacency. 'If it's in this location it must be OX-26'
I've yet to hear of OX-26 being put into a system instead of OM-15. If anyone knows differently I'd like to know about it.