I believe this is the single reason why Amazon dominates e-commerce. They were the first popular online store and so everyone have accounts with Amazon and so ordering is simple. They even have a one-click option which is a bad idea personally because it’s too easy.
The problem is checkout will always be hard no matter how smart is the form. I just don’t want to fill out the form. This becomes even more important for older ppl who refuses to fill the form even to save a few bucks.
Basically, the easiest checkout is not having to fill out anything and that only works when you saved your info. For even less computer savvy ppl, Alexa makes it even easier with voice orders however I always prefer to order via computer because I like to see what I’m ordering.