It's simple.
In the beginnings, growth was in developed markets, where most people already have a PC and TV. They have plenty of large screens around them, that the phone is just a secondary or tertiary screen. It doesn't have to be large, so smaller is preferred.
Fast forward today, developed markets are saturated. The growth now is in emerging markets, where many people don't even have a computer, and their TV was old and small. The smartphone is literally their ever first computer, or even their only device for productivity and entertainment. Thus the larger screen provides better user experience, and thus the demand is for the largest screen for the dollar. Even $100 Android phones are at least 6.5" or larger.
Some people in the developed markets may not understand it and feels like the phones are going too large. But Apple is a global for profit company where the actual growth in its revenue is in markets like China and Asia, and the demand for larger sized phones are real. Best selling Android so far is the S22 Ultra. The market speaks for itself.