Was it small capacity, mediocre cleaning results, expensive production costs, reliability issues?
I don't know for sure but Apex wasn't a major company like GE, GM/Frigidaire, Whirlpool, etc so I suspect they didn't have the resources and reach of the big guys.
My guess is that cleaning results in the Apex back then were on par with front loaders of the time which were below the average top loader due to the fact that low sudsing detergents in the early and mid 1950s weren't perfected as they are now. I'm shocked at times how well the Apex cleans stained items when I use good 21st century detergent such as Tide Free and Clear. When I use a vintage high sudsing detergent the results are not as good.
The owners manual to my '53 Apex says about detergents:
Synthetic detergents are of two kinds, non-sudsing and sudsing. Since suds tend to cushion the washing action, the non-sudsing synthetic detergents (such as "ALL", "SPIN", "SNAP", etc.) are especially efficient for washing heavily soiled or greasy clothes. Non-sudsing brands of synthetic detergents can usually be purchased in appliance or department stores, if they can not be found at the local grocery store.
The sudsing-type synthetic detergents (such as "TIDE", "SURF", "FAB", etc.) have decidedly improved cleansing qualities over soap products. They are recommended for washing clothes of average, or light soil. However, because their profuse suds tend somewhat to cushion the washing action, the non-sudsing detergents mentioned in the previous paragraph should be used if the sudsing-type (along with pre-soaking the clothes) does not achieve satisfactory results when washing heavily soiled or greasy clothes.
Apex strongly recommends the preferential use of synthetic detergents. However, if a soap powder is used when washing with the WASH·A·MATIC, then a very effective water conditioner, marketed by many leading grocery stores under the trade name, "Calgon", should be added to the soap powder to obtain satisfactory washing results and to prevent the deposit of soap curds on the clothes. "Calgon" performs the function of softening the water and, in addition, freeing the soap to remove soil from the clothes. Moreover, when "Calgon" is added to the soap powder, or added to a synthetic detergent as well, it will be found that less soap or detergent is required.