Wasn't the XR quite popular? I believe it convinced many of the 4.7"-phone owners to get an X-factor phone.
Actually it seems iPhone XR sales did pick up, but Apple had to further reduce the prices to drive sales.
https://m.economictimes.com/tech/hardware/apple-gets-the-mes...
Not sure if that means people can be bought or wether people really were just price sensitive.
Apple seems to believe its cost that keeps the SE relevant, and tried to tap the market with the XR... but very few budged it seems.