I remember when the refrain used to be "adventures don't sell, because only DMs buy them." Now we've apparently come around to "player options don't sell." Soon the circle will be complete!
All joking aside though, ever since the Hasbro era of D&D began (i.e. 1999), the idea that any iteration of D&D hasn't "maintained profitability" has gone out the window, because Hasbro's target has never been simply taking in more money than they spent. Rather, it's about ROI (return on investment). D&D has always been profitable in the Hasbro era, but it's rarely been profitable
enough for its corporate overlords.
I'm not a business executive, but I'm given to understand (mostly from a Gen Con seminar I was at several years ago, where James Lowder spoke about this topic) that corporations of Hasbro's size don't judge ventures by whether or not they turn a profit, but whether they turn enough of a profit to be worth their time. If they're only earning (my random example, here) $10 for every $1 they spend, then whereas you or I would think of that as wildly successful, they think of it as a failed investment, because that $1 could be earning them $100 somewhere else. That's part of the reason why they eventually shuttered the novels division of WotC, which was earning more money than it spent at the time it was closed down.
As for whether or not there's a segment of TTRPG players who will consistently buy crunch-filled supplements, we already know that there are, and that it's sustainable: that's how Paizo
stays in business. If they've been able to keep themselves going for well over a decade (sitting as the #2 RPG company in the business for almost that entire time by most accounts) using that model, then it's clearly not unsustainable or lacking in profitability.
Really, Paizo has overturned a lot of "conventional wisdom" in the RPG space. They have multiple lines of prefab adventures, proving that adventures sell. They put out consistent crunch-heavy books, proving that there's a market for them. And they kept 3.5 alive (counting PF1 as a form of 3.5) for over a decade after WotC moved on from it, proving that there was a significant portion of the player base who liked that system and didn't want to let it go.
WotC's leaving 3.5 behind wasn't due to any issues with the system, or with players deciding they were tired of the game. It was because they (WotC/Hasbro) wanted it to make more money than it was making, the same way that 5E is now being called "undermonetized" despite its success.
To summarize, it's not about profitability; it's about profit maximization.