Not at all. Some declines were due to external circumstances that were totally out of control of the software house. For example, puzzle/training games on console, following the rise of cheaper substitutes on mobile devices and digital channels. High-quality and well-positioned franchises couldn't compete with similar products sold at a much lower price. There was a shock in consumer preferences which couldn't be controlled. Or think about the drop between Pokémon RGB and Pokémon GS (around 2 million units), which was physiological given how much the former sold---numbers that couldn't have been replicated any under circumstance. Sometimes declines occur because the franchise itself loses popularity, without the software house being able to do anything. Think about the Run for Money series by Namco Bandai on 3DS. It sold incredibly well on the wave of the TV show but when the TV show started to become less popular, the series start to lose sales. This was totally outside the control of Namco Bandai, which in fact managed well the franchise with regular entries and increasing quality across them.
Then they could just have released the games on mobile instead. They didnt have to release those games on consoles. Or make sure that people were still interested in Run For Money. The interest was there at some time, the same goes for Pokemon at those levels, so technically we can argue that things could be done differently to maintain that, and that ties into maintaining something. I think this is a lot easier said than done however, so i wouldnt expect everyone to be able to be able to pull something like this off, and i agree that these are reasons that are valid. But what you say in this quote is a key to my argument:
Sometimes declines occur because the franchise itself loses popularity, without the software house being able to do anything..
This also applies to gaming franchises as well. I mentioned earlier that even if Polyphony Digital had made "the world's greatest racing sim", i still think there would be a decline. To me, it seems that you think that GT is immune to these reasons, and what is the reason for that? If Pokemon can drop in sales just because "sales couldnt be replicated", this is something that can happen to any franchise.
I guess i should added "as much". I can still enjoy RTS, but my interest is lower now. You never felt the lack/decrease i interest in something gaming related?
But regardless, my point was just that many people have moved over to gaming pretty much exclusively on mobile platforms instead, and this means less potential consumers. GT is/was a more casual game (appealed to everyone), so games like this can easily be affected by this change in the market. This is also the main reason why dedicated gaming hardware have declined over the years as well.
The point is that, Gran Turismo survived with huge sales across 15 years, 3 generations and 5 mainline entries (and plenty of demos, spin-offs and such) showing that userbase was faithful and wasn't tired of the formula. You don't lose 6m units across the board for external reason/consumer shocks only.
Sure, i've never ment to say that this is the only reason. I agree that there could be done things differently that might have lead to better sales. GT Sports being online focused is also an gamble for the sales. Its not only because the lack of popularity, i fully agree. My main point is just that lack of interest can also also be one of the bigger reasons. Things changes as time goes by. How things were 10 years ago, or even 5 years ago, this doesnt necessarily apply today.
Racing sims can't sustain 10m sales in today's market strictly because Sony wasn't able to manage the GT franchise well enough.
I disagree. GT6 was a "traditional" GT game, and not limited by design, as far as i know. I cant see that the only reason for why GT6 sold much less than GT5 is because it was released at the launch of the PS4. Those people still had a PS3 at the time, and it shows that they werent faithful to the serie. And as mentioned, GT6 still saw a big decline in Japan despite PS4 not coming out before months later.
I do however believe that GT6 could have seen higher sales if being released earlier, but i still believe that a noticeably drop would have been there without heavy bundling. Its the same with GT Sports. Sony can start bundling the game heavily to achieve higher sales numbers, but the days where you basically have 10 million people interested in the GT franchise and want to buy the game seperately, i'm pretty sure those days are over, at least for the time being.
EDIT: I added some text.