It became more common when they started getting most orders from the web page, but even before that, over the phone you could order whatever toppings you want. (They just didn't advertise all the options back then.) They also gave the option of different toppings on left and right to keep a family happy when they have different tastes. And since it's now on a web page, they don't have to spend time on the phone while you explain it to them.

But even back in the 90's, my dad ordered a pizza with half no cheese. (He still had the sauce though.)