First of all, requiring lots of memory and requiring lots of performance are not always the same thing, for casual users a pile of browser tabs and a couple large office documents is enough to eat a significant portion of 8GB just by themselves.
Second of all, talking personally where I have heavier requirements than the typical casual user, I have a 2020 Air with 16GB of RAM, why isn't it for me? I wanted a machine that can do light dev work for personal projects (I have a beefier and soon to be upgraded machine through work, plus I can offload truly intensive stuff to the cloud, even for personal projects) but can handle loading up a few VMs, a pile of docker containers, a lot of browser tabs, or all three. I also didn't want the touchbar. The air works great for my needs, it wouldnt work as great with 8GB of RAM
Third of all, despite the two becoming closer in some ways including silicon and some application frameworks now, the use cases are not the same. The big difference being people expect to be able to multitask and have things just work in the background way more on a laptop than on an iPad - that requires more RAM
tl;dr you have no idea what you're talking about.