First, and I don't mean to be pedantic, I'm sure you know this but just want to clarify, putting absolutes on things like saying no one buys something is almost always false. Very few people comparatively sure, but when it comes to capitalist greed these differences matter. Anyway..

Sure they'll miss a fiscal year or two here and there. But in the case of iPhones, I can assure you that if Apple calculated that the iPhone was going to continue to not sell well and would hurt their profits to continue manufacturing, I probably wouldn't be able to hit the button on a stopwatch fast enough to measure how quickly they would shut down manufacturing. Keep in mind that there are indirect costs/profits involved in many things. e.g. The value of user data gathered by phones is absolutely accounted for, goes into profit calculations, and is probably worth more to the right people than you'd think. Apple is one of the richest, most profitable companies in the world despite releasing what we would consider to be flops several times over the years. Apple released a video game console (the Pippin) in 1996 to compete with the OG PlayStation. They brought it to the US in '97 and pulled the plug the same year. The PlayStation released in '94 and sold well through the release of the PS2 in 2000 for comparison. A colossal flop from Apple that was nixed in merely a year.

A perfect example of the indirect profits that a product can accrue is when Google was initially getting into the tablet OS market some years back (around 2011 I think is when this specific "deal" was in place). They purposely sold the first Nexus tablet at cost/at a loss, paired with a "free" gift card for the Play store; on the condition that you had to add other payment info to your Play store account. A common tactic that other online vendors use because the statistics show that you are much more likely to spend money once you've already added and saved a payment method. Google didn't require people to actually use the added payment info, and as far as I'm aware they didn't even require you to keep the payment info saved for future purposes. They only required that you save your debit/credit card in order to use your "free" Play store credit. All because the biggest hurdle to getting people to spend online is/was getting them to give their debit/credit card info to the payment vendor. They correctly predicted that when offered store credit, consumers would not only give Google their payment card info, but also not bother deleting said payment info after they added the credit from the Play store gift card. Whatever the reasons may be, whether it be because you don't trust a website, it's more convenient to buy elsewhere, etc. and whatever the store may be, once you've added payment info you are statistically unlikely to subsequently remove that info and more likely to purchase there again in the future. Gotta love it.. but alas even my bitter ass is not immune from these tactics.

As for fidget spinners, I suspect the sheer excess supply from people trying to cash in on the craze has basically cemented them as a permanent item on shelves. I remember reading stories of "normal" people that bought literal warehouses full of the things because during the height of the fidget frenzy the markup on them was insane. And then other people presumably bought up that excess supply for pennies on the dollar when the trend was dying. The capitalists that initially jumped on the profit train when spinners were trending were either successful and took their profits and left the bag holders, or were bag holders that accepted their losses by selling in bulk to someone willing to try selling them.

That went a bit longer than I intended.. In short, even flops and niche items that don't sell very well can still be profitable. I would advise against doubting the ability of greedy people/corporations to extract every possible fraction of a cent in their pursuit of profit.