Well, I built the computer I'm using right now when I was 12, so...
Build a computer? In
THIS economy? What makes you think your experiences are universal?
I don't know how old you are today, but the home computer landscape has changed a lot in the past half-decade. Maybe in 2012 it was common for households to have one laptop per person, but with the rise of low-cost smart devices it's more common for kids to have their own phones or tablets instead, often handed down from older family members. The concept of a "shared family PC" in general is getting antiquated, too. Additionally, if a kid does have their own computer it's usually something cheap or something provided by their school, hence all the Chromebook users on this messageboard.
Not to mention that a lot of community members are also from countries where PC parts cost way more than you'd think they would. The USA isn't the only country in the world. Many developing countries even skipped home computers entirely and jumped straight to low-end, low-cost Android devices. The popularity of games like PUBG Mobile didn't come from nowhere, y'know.
Hell, I'm from Australia and PC parts are bloody expensive here, and "cheap" laptops cost you like three times as much as a half-decent Android device. My current phone cost AU$200 and plays Mario Kart Tour fairly well. AU$700 will get you a slow-as-molasses laptop that can't even run YouTube properly.
The market is changing. That's why these requests keep popping up.