I’m someone with relatively small hands, plus I want my phone to be on the smaller side since I prefer to use my tablet/computer/tv to watch content. But this trend where many manufacturers tend to keep futures away from smaller phones to drive people to bigger phones is driving me crazy and really makes it hard for me to buy a new phone. I can understand not having everything like maybe a periscope lens or something else that is cost etc. but not to this level. Like take Samsung for example: S24 lacks uwb, 45w, a 1440p display, has a lower amount of ram and storage. Why? Why can’t the s24 have faster charging or uwb? Why is there no 512 version and why does it have to start with 128gb storage? Is it not a flagship? It costs 949€ in my place! Why do I have to give 200€ more to get the s24+ just to get these simple features? I don’t want a bigger phone! Google does the same! No uwb, no thermometer sensor, no telephoto lens. And don’t get me started with all the software features google is keeping for the 8 pro like they don’t have the same processor. Why? Are they cheap? No they are not. I’m just really annoyed by this cause I really don’t want such a big phone.
One of the questions asked (“Why do I have to give 200€ more to get the s24+ just to get these simple features?”) was comparing S24 to S24+. While I have not looked it up, traditionally those versions range from SXY (small) to SXY+ (medium) and SXY Ultra (large), but are otherwise the same phone, so I would be surprised to hear if e.g. the S24 was foldable but the S24+ was not?
As for whether it gets more expensive to make something foldable vs. to make something more compact, I suspect the devil is in the details, so ymmv and you just kinda take each option as it comes. Other factors may help mitigate those costs e.g. a younger company trying to break into the big leagues might try to give phones away for virtually no profits in exchange for their increased market penetration (e.g. OnePlus used to be somewhat this way, now they are in the big leagues, more or less).
But your other point, about more materials: no, I believe that it’s more complex than that b/c it’s the effort of fitting things into tighter spaces that is more constraining. Imagine packing for a long vacation and/or a job interview at a far-away place and you get the idea - if you can fit everything into one suitcase that’s good, but a tiny backpack is much harder to accomplish, and to take nothing and just live with what you can carry on your body alone is REALLY tough! (especially if you want all the normal features like not smelling bad) i.e. the materials costs, while not negligible, have not been the driving/limiting force for many years. At least according to everything that I have read, but I am no phone manufacturer!:-)