Because it isn’t finalized yet

 Is it final at irs.gov yet? Doubtful.

Because it's always one of the later forms to be finalized by Intuit.  They are busy with 1040 duties.  Can't be everywhere at once, you know.  A similar question is why haven't my 1120-S clients just printed out a year-end report for me, since that's all the data needed for doing the return (at least to get the draft started).  The answer is the same -- because they are busy with other stuff.  

Yes, it is final there, and the schedules seem to be available also. 

https://www.irs.gov/pub/irs-pdf/f1120s.pdf

Even the when forms will be available is not yet available! https://proconnect.intuit.com/tax-online/forms-finder/