I recently read an interview with a woman that fought for the USSR in WW2 and is now living in Iceland. She had to fake documents to get herself out of a munitions factory line job in order to get to the front lines. Was it a policy in the Soviet Union to ban factory workers from fighting? Was it in order to stop information leaking out?
Its generally all about balancing the need to fill bodies in uniform, but also to not completely shutdown crucial industries. Drafting your entire workforce and then running out of shells or food isnt a winning formula. Even in the dark days of 1941-42 for the USSR it was still not productive to close all the factories to enlist the men and women in them. And less stressed societies like the US home front were very conscious of how many men they drafted each month to keep the process as orderly as possible without being counterproductive.
In most industrial nations when it comes time for conscription you will have exemptions carved out for crucial war industries. And to stave off possible harsh feelings, a propoganda effort highlighting the home front's industrial contributions to victory.
For instance in the US men could get Selective Service classifications of II-A,B, or C. Which corresponded to National Security/Health and Safety Workers,, critical war industry workers, or agricultural workers respectively all of which were in line to be deferred from compulsory service.