From what I have heard from other developers, MS/Asobo contracted them to build planes for the 40th Anniversary.
Some of these planes were already partially complete, and had been announced publicly as payware releases.
Planes like the DC-3 and the Beaver would have had more models if released as payware, but for the 40th Anniversary release, they were only tasked with making the models from prior MSFS titles (especially 2004’s Century of Flight).
MS/Asobo’s contract will not allow developers to release payware versions of the planes they contracted with MS/Asobo to release for the 40th Anniversary. And developers will lose money by continuing to add new models for a contract that has already been fulfilled to MS/Asobo’s liking. MS/Asobo wanted exclusive rights to these planes and paid developers for said exclusivity. This means Blackbird/MilViz are not allowed to make and sell a turbo or tundra Beaver, and the folks at Aeroplane Haven are not allowed to release a payware military version of the DC-3 because they already contractually agreed to sell the planes for this SU11 release, so now, Asobo gets those exclusive models and the developers are not allowed to double dip for profit after they were already paid for exclusivity.
So, it is safe to say we would have got more plane in a couple cases if we had payed the developers full price for an addon, but the developers got enough money from MS/Asobo instead, to make it worthwhile for them to contract their planes out for release in a simpler form, to a larger user base, for the 40th Anniversary edition of MSFS, and now they are bound by contract to keep those models exclusive to MS/Asobo, who never contracted them to make more models or versions of their plane. They gave their client, MS/Asobo, what they were contracted to provide, which was less than they intended to develop had they released these planes (likely at a later date) to the public as payware.
TLDR: AH wasn’t contracted to make a military version of the DC-3 for SU11, so they wouldn’t have made any more money if they did. They were contracted to provide MS/Asobo a working DC-3, which they delivered, and are likely contracted to fix bugs as needed, but they aren’t allowed to make a payware version of any variant of that model. Their exclusivity contract with MS/Asobo will not allow it.