QR yield management is very "agressive" in opening fare bucket availability, including in the very long run. Not a very good system in my opinion.

Of course, they tend to reduce availability on much-cheaper married segments compared to 2 single segments.
In your case QR1368 JNB-DOH is already only selling J4C0D0I0 as a standalone flight. Ten months ahead , this is probably caused by the fact that they already sold a few Biz seats and the plane is a small capacity 24 J. This can change in the next 10 months, or not.

Weird yield management. But QR got so burnt by selling awards during pandemic that prevented them from selling expensive casf fares once it ended, that they probably set their yield management IT with the strictest parameters.