As has been mentioned enough now, the reason is that movies are following symphonies, not the other way around.

As a fun fact, the same goes for other media, like computer games: these used to not have symphonic music in the distant 8-bit and 16-bit era simply because the old machines were not capable of reproducing this kind of fidelity. Later, as the audio chips became ever more powerful, we had a middle ground where games could use MIDI and later realtime sample mixing to approach symphonic pieces quite successfully. Eventually, today, most expensive (AA/AAA) games have music scores that are symphonic - sometimes recorded by actual orchestras (famously, check out Austin Wintory's score to the game Journey, like this live recording behind-the-scenes).

Also it just so happens that adapting more current music (rock, metal etc.) to pure symphonic versions seems to be quite popular. Or, speaking of which, even mixtures like Symphonic Metal.

It seems that this kind of music is indeed timeless, and while there certainly are movies or games that do not use such scores (e.g., the original "Highlander" with its predominantly Glam-Rock score by Queen, or "Thor 3" with its hilarious Led Zeppelin intro, or any number of movies with mixed OSTs), most do. Maybe it's the capability of these instruments to at the same time stay in the background in a quite restrained manner, just filling out some unwanted quiet, but then also to really play a role as the foreground star (i.e., some scenes in "Interstellar" with the absolutely bombastic horns from Hans Zimmer). You can get both something that is almost invisible/inaudible; and something which is also grating your nerves (the classic high tension strings, for example in the old Hitchcock movies). Symphonic music seems to be easily able to encompass all emotions quite successfully.

As has been mentioned enough now, the reason is that movies are following symphonies, not the other way around.

As a fun fact, the same goes for other media, like computer games: these used to not have symphonic music in the distant 8-bit and 16-bit era simply because the old machines were not capable of reproducing this kind of fidelity. Later, as the audio chips became ever more powerful, we had a middle ground where games could use MIDI and later realtime sample mixing to approach symphonic pieces quite successfully. Eventually, today, most expensive (AA/AAA) games have music scores that are symphonic - sometimes recorded by actual orchestras (famously, check out Austin Wintory's score to the game Journey, like this live recording behind-the-scenes).

Also it just so happens that adapting more current music (rock, metal etc.) to pure symphonic versions seems to be quite popular. Or, speaking of which, even mixtures like Symphonic Metal.

It seems that this kind of music is indeed timeless, and while there certainly are movies or games that do not use such scores (e.g., the original "Highlander" with its predominantly Glam-Rock score by Queen, or "Thor 3" with its hilarious Led Zeppelin intro, or any number of movies with mixed OSTs), most do. Maybe it's the capability of these instruments to at the same time stay in the background in a quite restrained manner, just filling out some unwanted quiet, but then also to really play a role as the foreground star (i.e., some scenes in "Interstellar" with the absolutely bombastic horns from Hans Zimmer). You can get both something that is almost invisible/inaudible; and something which is completely grating your nerves (the classic high tension strings, for example in the old Hitchcock movies). Symphonic music seems to be easily able to encompass all emotions quite successfully.