Transport museums in the UK are fascinating because they are full of machines that didn't solve any problem satisfactorily. My local museum has the bicycle well represented along with much else of the times, early lawn mowers, sewing machines and everything else.
The boss of Trek says the product (the bicycle) has been fit for purpose for a century. I think he is right, even though I am not riding anything before 1989, when indexed gears, decent brakes and many user improvements came along thanks to Shimano, a favourable Yen and the mountain bike 'fad'.
As for 'beats walking', the pre-war roadsters with nickel plated steel, hub gears, lights, a pump, mudguards and big springs in the seat, on OG Dunlop cotton sidewall tyres, I would take the bicycle any day over walking, particularly if the streets are full of horse manure.
This was the biggest time for cycling in the UK, the car took over after the war. Meanwhile, in the USA, the car had ousted the bicycle, street car and train to a huge extent, putting them on life support.
Back to the transport museum, the amount of experimentation for things like brakes is wild, with many unlikely designs after WW2, when I expected something more recognisable. Then there was no innovation from Europe apart from minor iterative improvement until the Japanese showed everyone how it is done, with Shimano being the dominant player, with Suntour as the plucky underdog. Innovation was then like the latte 90s for PC's, everything would be out of date within six months and you would need to upgrade.
There was nobody with a master plan, guiding the cycling boom along, it was just a convergence of shared interests, with 'mountain biking' being a response to bicycles no longer being welcome on the roads.
BMX also played a part, as that 'fad' resulted in chro-moly 4130 steel frames, welded in the Taiwanese Province (tm) rather the usual lugs and brazing used in the West. The BMX factories provided the capacity and they had the tooling for mountain bikes, so that played a part in the 'secret plan' to engineer a boom (as if).
In the context of mountains of machinery and incredible innovation of peak Industrial Revolution, and my personal recollection of the MTB boom, I don't believe there is a 'lived silver thread' that explains all, only historians can weave together a narrative that sort of makes sense.
Incidentally, the bicycle is still the cradle of innovation. Clothing is an interesting area, typically, in a given era, cycle clothing, including shoes, helmet, sun glasses, gloves and 'lycra' is on a different technology level to anything the likes of Nike or Adidas are doing. Hydro-formed aluminium, carbon fibre and much else is far more advanced on two wheels than on four, where the vehicle weight is 100x lighter.