That says to me that the volume of sales is in the 2GB variant.
Perhaps for most people the 4GB is too hot and the 1GB too cold… :)
Edit: I love that Ice Tower cooler, hadn't seen that before. Want one for my Pi now, but at £20 it seems a bit extravagant.
Oh and there's even a horizontal version with twin direct contact heatpipes :D So cute!
https://www.amazon.co.uk/GeeekPi-Raspberry-Low-profile-Horizontal-Heatsink/dp/B07ZV6JDNL/What I really want is a Pi in ITX format