The wider the panel the, the smaller area it has, while still preserving the diagonal (i.e. 14" 16:9 has smaller area than 14" 16:10), allowing more panels to be cut from the same material and increasing the yields in case of material defects.

I.e. making of wider panels is cheaper, and because in advertisement there's diagonal and not area, it still allows advertising in a way that doesn't put the manufacturer or oem to disadvantage.

Popularity has nothing to do with why its more popular. The industry decided as a whole to go with 16:9 screens due to them costing less, and consumers had no choice. Similar to how most flagship smartphones have lost their headphone jacks even though no customer is running to buy a phone just because it doesn't have a headphone jack.

But consumers do run for ever thinner devices, and a 3.5mm jack will always make the device at least 4mm high (probably more to account for front display and backside assembly).

And when they got too thin and started bending in pockets folks complained until they got sturdier and thicker again.