Some people (as you) like small phones. In the other hand, the fact is that a lot of people (common people, not necessarily tech related) is buying year to year even bigger phones. The only way Apple can satisfy the buyers who need a small form factor, as well as the ones who want a bigger screen (when unfolded), at the same time and even with the very same phone is precisely with a flip iPhone.
The current trend for which many people are looking for bigger screens year to year has a physical limit that will be reached when the large phones were not able to be easily pocketable any more. So unfolding a pocketable device means that it automatically double its size, this way if you have a 4 inches folded device, unfolded it will reach 8 inches. 4 inches is shorter than the Mini, while 8 inches is larger than the Plus or Max.
Obviously Apple has taken its time because we can be sure that they have been perfectioning the folding screens to not have an ugly and notorious crease.