This is a customer base where most purchased $1,200+ plus weapons in current day prices (premium AK level customers). Many of the early gen (I'd guess at least 2/3rds of VZ58's sold) have 15.5" barrels requiring fixed muzzle devices -- the later ones and VZ2008s do not however.
Basically, no one else is serving this community and weapon system on the suppressor front, and due to essentially having a captive audience (especially for those who would "permanently" affix their muzzle device) making muzzle devices provides them with great upsell (i.e., their suppressor line) IF they have the sense to first make the muzzle devices available. I don't see how they could possibly lose money. Especially since it's just a matter of threading in a different direction AND they're muzzle devices are full-priced at $90, definitely not loss-leaders intended to foster greater revenues through upsells.