Well they would have had to build the Cromwell to build the Centurion since it was the same automotive system so I can see why that didn't happen.

Although Cromwell's only ever equipped 6 battalions so from a certain perspective the UK almost did drop the building of indiginous Medium Tanks concentrating on Churchill's (and there were not many of those either; only 3/8 of the number they wanted on D Day) converting Firefly's/M10's and so on safe in the knowledge Uncle Sam was on the case and the M4's would flood in.