@willk_1230 So if by eligible Minor Factories... you mean the one in Novgorod and the one in Volgograd... then it is because neither is eligible to be up-graded.
"Major industrial complexes can be built only in originally
controlled (not captured) territories with an IPC value of
3 or higher." Page 23 Restictions on Placement Pragraph 4.
Here is a link to the manual for your reference....
https://www.axisandallies.org/wp-content/uploads/2011/12/Axis-Allies-Europe-1940-Second-Edition.pdf