The fact uk invented the rail network is it's blessing and curse.
The infrastructure was developed iteratively, and by many small competing networks.
With no ongoing effort to improve interconnectivity since then, we are now in the position of having an archaic network that is extremely difficult to maintain let alone upgrade.
I worked in signaling design 5 years ago, and as a future thinking techy I was appalled at the state of it.
Drawings are still 80% on old brown plastic sheets and need electric erasers to run out old connections to draw new.
The big location cabinets are choc full of actual relays for the logic - the things that preceded transistors.
I could go on, but the fact is it's insanely expensive to do anything, and the ingrained infrastructure is not conducive to being torn up and rebuilt. Look at the hs2 debacle, how hard would it be to get the whole country to agree to similar, even if we had the money.
It's a terrible state, but rather than blame the UK for being so bad, I'm slightly dumbfounded how other countries are so good