I'm not particularly aware that the RAF had any Skymasters at all. Loads of DC3s (which BOAC did take) but not DC4s.
There weren't a lot of Yorks built, and the RAF seems to have wanted to keep those that were around. The Lancaster (and the Halifax) were however readily available for conversion. There were very few commercial passengers at this time, mostly government personnel. The York seems to have had the same payload as the Lancaster (it did after all have the same engines), just a greater space to put it in. At this perod carriage of mail was as important, if not more so, than the carriage of passengers.
Minimal number of Constellations (and Stratocruisers) was all about supporting British types and British manufacturing industry. The civil servants could not understand that the Tudor, the Hermes, and in fact just about every post-war attempt before the Viscount, were complete crocks. The Hermes cruisd with an attitude of about 20 degrees nose-upwards which ruined its economics and range (I believe this led to some passing crews overseas asking if everything was OK). Quite how such an elementary error could be made by anyone who got past Aircraft Design 1.01 at college I cannot imagine.
By the way, in case you think I'm being unpatriotic, what the French commercial manufacturing industry turned out between 1945 and the Caravelle was notably worse ! There were also some poor attempts from the USA.