So...where 're all the "Danger is near" music ?

[Romulator]

Besides that, trailers can be manipulated. For all we know, Frictional Games may have used "acting" monsters which do not use the danger music in most of their trailers.

What I sent is not the trailer, it's a gameplay from the demo though.

It was more a generic mention - gameplay videos, trailers, teasers, etc. All of their sounds can be changed either within the game's code or during the editing process. It can be done to exclude some features, such as the "danger" or "is near" music as the OP mentions