As the username suggests I work in TV

I'm a broadcast engineer.
Frankly on programmes like this there is no need for background music at all. It's only added to add drama which, in reality, isn't required. Especially when combined with noisy environments such as railways.
The nature of filming means they'll likely have used a shotgun (directional) mic on a boom & blimp setup (furry thing on a pole) & these will make any sound in the direction the mic is pointed very loud indeed (Sennheiser & Rode are most popular - we use the Rode NTG4), and then the audio will be "compressed" in post - that's compressed as in dynamic audio compression rather than MP3 or any other file compression which will actually bring up the ambient noise if done badly, which it usually is. And certain noises take something like RX Post tools to fix.
Then they add background music. And the audio is compressed again. Then at play out, as part of the broadcast chain, the audio is processed which compresses it once more & maybe applies an EQ curve - processing is much more complex than this for both TV & Radio and is actually a specialist subject of mine.
Anyway, the resulting final mix you hear if all this is badly done, and that badly done-ness starts right at acquisition & every part of the chain after that affects it, is a compressed mush where everything is the same level & results in you hearing what you heard on that programme.
Technical standards in the industry are utterly terrible these days, BBC still care, but even then things slip. There ARE standards, but they're not really followed very well, since now everyone who can press a bloody record button is suddenly a documentary maker.....legends in their own flaming lunchtime. Whilst we production professionals struggle for work, fight to get paid & watch the terrible rubbish being broadcast noticing all the problems.
Sorry, that turned into a rant but now at least you know why it's so bad