>>9804465Probably to keep things cost-effective. Children generally don't care about scale either - it never even entered my mind growing up. The little 1/72 tanks were light tanks, any between that and 1/48 were medium, 1/48 (aka the Timmee Patton) and above were the heavy tanks - imagination did the rest.
There are brands producing vehicles closer to typical army men scale but they tend to be expensive and/or hard to come by.