Here's the reason (as above poster stated)...many more Inlands made than any other.
M1 Carbine Production
Inland Manufacturing Division, G.M.C...........2,632,097 43.0%
Winchester Repeating Arms Co.....................828,059 13.5%
Underwood-Elliot-Fisher Co..........................545,616 8.9%
Saginaw Steering Gear Div., G.M.C...............517,212 8.5%
National Postal Meter Co.............................413,017 6.8%
Quality Hardware & Machine Co....................359,666 5.9%
International Business Machines Corp (IBM)...346,500 5.7%
Standard Products Co.................................247,160 4.0%
Rock-Ola Co..............................................228,500 3.7%
Total: 6,221,220