Why was the M-36 tank destroyer not produced as a tank?

It might be argued that in the end it was, the 90mm high velocity gun of the M36 appearing in combat on March 7, 1945 as the main armament of M26 Pershing Tank. The dates are critical in explaining what American tank destroyers and tanks were in combat in WW2. There was a major race for development which forced decisions on temporary and compromise solutions. In 1940 American armored forces did not have a vehicle mounting even a low velocity 75 mm gun. In August 1940 there was a desire for a turret tank of at least this calibre, but the clash between need and engineering knowledge was such that the M3 (Lee/Grant) with the hull mounted gun was put into production. Similarly, as higher power guns were needed in the light of combat experience, the 76 mm, + 90mm, heavier, with larger breeches and heavier recoil, it was in the first instance quicker to produce vehicles of the tank destroyer configuration. Heavier guns often appeared first in assault gun format in the the Russian and German armies too. The British were probably least successful in their designs, but that the Archer was produced, and fought in Normandy and later with some success, demonstrates the pressure to get the guns on the battlefield fast, even in a "fudged" design For the rearward firing Archer: http://www.msu.edu/user/storto/britspg.htm. http://www.tankdestroyersociety.com/tank_destroyers_history.htm