If you look at distributor single-unit quantities, they are close in cost. If you look at hobbyist stores, they are the same price (or more expensive for the seven-segment version).
If you ask a factory in China to make you 1 million displays, the seven-segment version will be a lot cheaper. That's why new products use them. Even at 1k quantity from distributors, seven-segment displays are substantially cheaper.
Some Chinese display manufacturers are dumping lots of small, easy to use, postage stamp sized monochrome blue-white OLED at ~$1.5 apiece from 1 unit with free shipping, which had made it a viable replacement for 7-segments, couple power LEDs, even decorative logo displays, for small scale productions. It's not the case at all for real mass produced products, but not everyone is delivering thousands of units per month to Walmart.
I personally don't necessarily support "just go graphical" sentiment, but such local minima do exist.
I had considered that maybe new 7-segment displays aren't being made, so maybe they cost more for that reason, but even that doesn't seem like it'd be true.
How can that be true?