It's because modern client-side frameworks like react or vue use javascript for routing, and in fact storing every character in a form as you type it is a basic

It's because modern client-side frameworks like react or vue use javascript for routing, and in fact storing every character in a form as you type it is a basic design principle in such frameworks. If you are curious, you can install their respective dev tool extensions so you can tell at a glance which framework a website is using by checking which button lights up in the browser toolbar. I like the uBlock Origin toggle myself, aka the "naughty website gets no javascript" button.