Thinness has not been an issue in the last 10-15 years.
A thin phone is also very hard to hold, it kind of flips in your hand.
It's the difference between stated and revealed preference. Phones kept getting larger and larger because larger phones sold better.
Though apparently we have hit the sweet spot a while ago, as phone size is stable now.
There is no year in which the larger size sold better than the mainstream size. Ever.
You are literally just making shit up.
That claim is demonstrably false. Whether attendant facts like adjusting for price point lead to a subtler inference does not change the absolute fact that the proposition is not consistent with reality.
The claim is "larger phones sold better."
That claim is flatly, objectively false.