If you want to see official Valve maps decompiled, head over to this thread, you can find all the vmfs there. As for the other maps, they may be protected from decompiling (TopHATTwaffle had a video about it or something) but thats more likely to be something on your end. What are you using to decompile, what does the log say?
Some custom maps may have protective measures which prevent VMEX from decompiling the map. However, since it's 2017, you should be using BSPsource which is more updated.
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