That's the downside of any monolithic design vs chiplets and in general GPU revenue is weaker than CPU, per silicon die area.I think 505mm^2 N21 is nonsense.
That would give you 83 good dies per wafer. Even if they were all 6900XT and the 6900XT is 3080+5% it means AMD can look to charge around $700 per card. That is revenue of $58,100.
OTOH a wafer of Zen3 dies is 782 good CCDs. Even if all are used in 5600X's that would be a revenue of $230k.
A 500+ mm^2 GPU is far far far too costly for AMD when they can generate 4x the revenue by making Zen3 parts instead.
Edit To Add: The other option is that availability is like the 3080/3090, non existent.
EPYC is ramping like crazy lately for anyone who has noticed, VMs, datacenter and super computers all aboard. The beauty of Zen 2 or Zen 3 dies here is per wafer, their revenue is MASSIVELY more than anything AMD can get with gaming GPUs.
When your wafer is limited, you want to devote most of them to the higher revenue & profit products.