>>63831152
Also, that wasn't like the sole reason that gun was rejected, just one of them, it was overall not that much cheaper than the Thompson, which is the big pain which the army was looking to relieve during WW2.
The Thompson was a VERY expensive gun to make, the M1A1 was pretty well economized for what it was, but you could still go hell of a lot cheaper with other designs.

Slightly related, here's a Chinese Warlord Era clone of a 1921 Thompson, which has been converted to 7.62mm Tokarev