What's The Deal With Incompatible Browsers? (& How Can We Avoid Incompatibility Issues?)

I first noticed it with Pizza Hut's online-ordering program---it's been a while, but I think it was some 'issue' where the program got stuck on the 'finding a Pizza Hut near you'-function ... while I was using the Internet Explorer (IE) browser. But on the Google Chrome (GC) browser, it ran just-fine!

(Maybe it's a sign I'm "getting old," but I'm too impatient
to 'check-&-see if it works on IE' everytime I want to order
online. No, I pop-open my GC when I go to Pizza Hut's- or
any other-site I remember is going to freeze-up on IE.)
​

It's similar to the problem I frequently experience with sites that email me links which won't open in IE but open just-fine in GC. I understand that the programmers are using one-or-the-other browser, but don't they want their programs to be readible by ANY browser we might use?

And how can we programmers make sure our content is universally available?