I think a lot of the mods problems have to do with obsolescence. There are a lot of modders who've left, for various reasons, and their mods they made for SFP1 are now very buggy when using the latest SF2. The answer should be "don't use them", but people want to use plane X or terrain Y or effects Z and won't accept that. Instead, they blame TK for "screwing up SF2" so we have lots of people who either won't buy SF2 or bought one or 2 but now have reverted to SFP1 "where stuff works".
I still have old SFP1-based installs for things like ODS and OTC and a FE-pre Exp 1/Gold install for those early war WWI-planes. Sure, some of these will "just work" with SF2, but many require changes. Some are minor changes but some require a lot of work and if you're not a modder at heart but rather just want to fly but want to fly THAT plane you're going to be disappointed.
I knew a guy who owned all the 1st-gen titles but SFP1 and we played them MP from time to time, but he was a non-modder. He refused to read a readme, he refused to even literally spend 10 minutes thinking about how to mod. He wanted one-click installers for everything, and preferred the big ones like NF1-4 because that was a simple sequence of "double-click, point to install directory, click done, fly". I would tell him or even show him a screenshot for some new plane and he would be all interested...until he found the mod was in a zip file that had to be drag-n-dropped into multiple folders and heaven forbid weapons/decals/effects/etc had to go to! Dropping a plane into the aircraft directory was as far as he'd go, and if it was one of those instances where someone nested a folder in the zip (ie it had "plane/plane-A/cockpit" instead of "plane-A/cockpit" in the zip) so that it wouldn't work if dropped as-is into the aircraft directory, he was turned off. As a result, he mostly only played the stock games, and when SF2 came out without MP he just passed.
TK has to compete not with any particular game or sim, just with people's expectations. Even at $20, if he fails to deliver on that, he won't sell.
The problem is what people were fine with 5 yrs ago is now seen as insufficient by many, and let's face it but simmers are a stingy bunch. While they'll spend a lot for hardware like sticks or TrackIR, they HATE to spend on any sim but MSFS addons it seems. I mean, sims at $50 are seen as too expensive, when they cost $50 15 yrs ago?!??
DCS:A-10C going for $60 is an interesting experiment...how many will buy regardless of price vs those that only buy things $40 or less? At $60 they'll make the same amount for selling 100k copies as they would selling 150k at $40...but will the numbers break that way? Will they lose fewer customers at $60 than the amount they'll gain per copy? Only they will know.