I would like to add my view on this subject. I also miss having PDF/X1a-2001 for sending work for printers, yesterday I had to download Creative Cloud products although I like Affinity software.
You could consider different markets of buyers for Affinity, for example, Brazil would be a really big one because of the number of people in the country, about 212 million and low value of the local currency makes Adobe products 6 times more expensive compared to dolar, euro or pounds currencies.
You could counsider other countries outside the zone of Euro, Dolar and Pounds, (not only Brazil) because of numbers, there are buyers outside there and their needs would be to have a software that save files in PDF/X1a-2001. Many of these people do not speak English to come to this forum, maybe that is the reason there are not more posts about it.
I think that the software companies can easily benefit and profit from global markets. Why not taking care of this little detail, "PDF/X1a-2001"? Adobe and Corel are more aware of this feature and they keep it.