Believe it or not people use phones for different purposes. Some people carry phones in bags or purses where space not a not a big concern. Some people use their phones for work and a bigger screen is helpful in the process and for multitasking. Some people aren't rough with their phones either.

A fad doesn't last this long. We are on year 7 of foldables available in the mainstream and sales and production are only increasing. Every major OEM has at least foldable or is releasing one soon. 3D TV's were fully dead in 7 years for context.