Greenjacket is right, and there are many other factors.
This 'what if?' is often brought up in books along the lines of 'the Mosquito could carry as much as a B-17' which in itself isn't really fair; later Marks of Mosquito could carry as much as early B17s up to the E.
4000lb 'Cookie'-carrying Mossies actually appeared fairly late in the war ; the Lancasters could always carry 14,000lbs of mixed payload from their introduction.
Unfortunately, saturation was chosen due to the impossibility of precise night-time bomb-aiming and the 'Berlin express' Mosquitoes were only ever 'nuisance raiders', depriving the citizens of sleep. Mosquitoes could be supremely accurate during daytime but were very vulnerable to flak or,especially, Fw190 attack.
Also, one has to remember that British officialdom viewed the Mosquito with extreme scepticism from the outset; only with hindsight do we fully appreciate the aircrafts' multi-role virtuosity.
Finally, the question of production must arise. In the 1940s, Britain had a huge 'metal-bashing' industry for aircraft, cars and related components which could quickly turn to production of military aircraft. One of the brilliant facets of the Mosquito concept was to turn the redundant British woodworking industries to war production. However, there were limits and Mosquitoes needed special wood ; it takes time to grow more trees !
