Manufacturers don’t make displays under 6 inches available for purchase, with special cases (such as the iPhone Mini) being made under exclusive contracts. The best lead they have so far is to try to use displays designed for the front part of a foldable phone, but they’re yet to strike an agreement.
TIL that display manufacturers are also part of the reason why we aren’t getting small phones and why it’s probably even harder for manufacturers like Fairphone to make them.
People generally just want the biggest screen they can hold in their hands comfortably.
For most people that seems to have settled into the 6.5-6.7" range, depending on aspect ratio and bezels.