You could argue the same for all the passengers and freight that does travel by rail. Just pust them on the roads...
If you have a nice predictable flow (like commuters who do regular journeys every weekday, freight that needs delivering every Tuesday, leisure passengers who head for the shops/hills each weekend) then rail is great. Dependable bulk flows are what rail does best.
If you have an irregular flow or a short-notice demand then rail has never been particularly flexible. Not just the modern privatised railway, also British Rail, also the predecessor companies.
For example, look at the football fixtures for this coming Saturday. Middlesbrough are down at Cardiff. Might take hundreds of fans down, enough to fill a charter (especially given the lack of a direct train). But how do you run that service? Which drivers have route knowledge all the way and what stock is cleared all the way? How many paths should we keep empty through the various pinch-points and bottlenecks between Teesside and Wales? Sorry we can't accommodate increased services for local trains in York/ Sheffield/ Birmingham (etc) because we need them just in case the path might be useful for a "footex"? See also Blackburn fans going down to Reading, Hull fans going to Luton, Norwich fans going to Burnley, Brighton fans going to Newcastle... you could run
hundreds of footexes every weekend if it weren't for the inconvenient fact that the railway is full, we don't have the luxury of maintaining driver route knowledge on every bit of line in the UK at the same time and we can't leave hundreds of empty paths on a "just in case" basis.
If this were a delivery of one new train a week for the next fifty weeks then it might be worth getting a regular path sorted out, it might be worth route training the drivers and ensuring that every inch of the line was cleared for that size of stock. But it's going to be a haphazard "dribs and drabs" delivery of trains that will only be a temporary demand. The railway isn't flexible enough to cope with that (given that any path taken by such occasional trains is a path that could be used for regular clock face trains every hour of the daytime).
I've no problem with the suggestions that it'd be nice if rail were flexible enough to accommodate such services - wouldn't it be nice etc - what is frustrating is some on the thread (not a dig at anyone in particular...) who have ignored the explanations from those in the industry that things are a bit more complicated than a Thomas The Tank Engine episode, where the Fat Controller can click his fingers and some random slow freight can be squeezed in amongst the regular fast passenger services. Nor is it a model railway where you can rip up the "timetable" to run whatever you want - the days of Speedlink are long gone.
This Forum is a wonderful opportunity for those who don't work in the industry (like myself) to learn from those who do work in the industry about how things actually function, the problems that lay-people like me might not have considered etc. Not everyone seems to want to learn though. Really need to get away from this mindset that heavy rail is the answer to every problem (regenerating dilapidated towns, re-balancing the UK economy by cancelling Crossrail to spend the money in Manchester instead, solving climate change, providing millions of jobs to stimulate a post-Brexit recession, teaching people Gaelic...) - it's a big blunt tool that is great at what it does best but lacks the flexibility to tackle every problem - and sadly doesn't have the spare capacity to bend over backwards to suit a handful of short term deliveries of 195/331s.