With the rampant use of super cost-effective guardspam followed with no-tech call-ins, I have trouble finding the manpower for even 1 ISG. Let alone 2!
I see what you mean but I generaly observed that if (as OKW) you are using a doctrine which provides you with elite infantry - that you will buy for sure (for instance fallshirmjagers) - or you are using more than one obersoldaten squad, you will hardly be able to afford even one ISG.
Situation is quite different for doctrines like breaktrough or when I am relying just on volks sturms and mgs. In time, I find myself floating alot of manpower and guess what do I build?