Amazon is going to win heavily aren't they?

Or to put it another way, 3 out of maybe 10 of my computers can checkout at the newly updated Walmart.com. For Apple's Online store, it says "please call us to make an order". For an indie online bookstore I went too and few others, it says "your browser is not supported" please use a new browser where some devices can't use a new browser. And other websites consistently giving errors and not load things.

For 10 out of 10 computers, Amazon.com works.

Why are web developers doing this?

I grew up at a time where the obsession was IE6 and backwards compatibility was key so that no customer was left behind. I remember we did everything to make sure as much of our customers can access our websites with fallback towards more universal and generic HTML standards that have stood the test of time.

I'm a tech person, I have access to the latest and greatest. Many of my friends, parents, relatives do not.

Now, so many websites demand the most up to date browser to work correctly and shop and apparently gives you no choice except to use it or not shop at their store except, well, Amazon. So Amazon they shop.

What's going on here?