Another factor to consider:
The Lanc is not alone in being produced in large numbers, but having few flyable examples. The US B24 was produced in great numbers, but there are only two flyable examples of a bonafide B24 today, plus a couple of navy variants that were used as water bombers until they were retired. The B17, on the other hand, has around 12 flying examples today, with more under active restoration.
Postwar, a flying Lanc wasn't all that useful in commercial aviation, although the design was morphed into the Lancastrian airliner and York freighter. Lack of pressurization was a factor in commercial aviation, as the pressurized Lockheed Constellation airliner could operate more efficiently with less weather interference at high altitude.
The UK doesn't have the huge forests that justify water bombers to fight fires, while the US and Canada do... quite a few US WW2 bombers ended up in that role, as they could be had for peanuts, and were kept flying into the 1970's.
The smaller B25 was found to be fairly useful in civil aviation as a transport aircraft, so many flyable examples of it still exist today, while the faster but more difficult to operate B26 didn't adapt well to civil aviation and the only flying example was crashed a few years ago. The B17 was also found to be more adaptable to postwar military and commercial uses than the B24, which is one reason that so many more examples of the B17 still exist. You may remember the B17 that was used to pick up Sean Connery at the end of the film Thunderball... they were still being operated commercially in 1966.
Consequently, there are fewer examples to restore, and a much smaller pool of spares to assist in the restoration. A primary reason so many B17's have been restored is the much larger pool of restorable examples, and especially the larger pool of spares that were preserved to keep postwar and commercial B17's flying.
In my garage, I have a crate of brand new electrical switch boxes that my father bought from an electronics warehouse in the late 1960's. It wasn't until I rode on the Collings Foundation B17, that I found out what those boxes were: they are the switch boxes for the intercom on a B17, one for each crew station. That's why they have a big fat paddle for the switch: to be used while wearing heavy gloves.
Same for P51's... kept operational into the 1980's by a few air forces, so a good pool of spare parts can be had. Also true of the F4U Corsair, more flyable examples of it exist than the more numerous F6F Hellcat, because the Corsair was kept operational into the 1950's as a ground attack aircraft. The Grummman Avenger torpedo bomber was also found to be useful as a crop duster and transport aircraft, so quite a few flyable examples exist today.
Spitfires were widely distributed to other nations after the war, which may account for the high number of flyable examples. Egypt kept a number of Spitfires operational in the 1950's, that clashed with the Israeli BF109's that Israel had concocted in a Czech factory. The Hurricane wasn't widely distributed postwar, so it, like the US P47, has few examples operating today.
WW2 aircraft use up spares at a frightening rate. If they aren't available, they have to be made by hand... very expensive.
Because the Lanc, like the B24, B26, and F6F wasn't efficient in a civil or military application post war, a large number of them and their storehouses of spares were scrapped quickly. The warbirds that fly in the greatest numbers today also happen to be those that were found to be useful postwar.