18650 made sense, and it was economical, because there were multiple suppliers for it. If you didn't like the pricing of the 18650 of supplier A, you could turn to supplier B and ask them a quote. You could pressure them to give you better pricing by pitting them against each other. Pouch cells are custom size. If you ask B to make you pouch cell in X size, they are going to tell you that you need to send them millions first, to set up or adopt the production line for you. And maybe you need to commit buying millions of cells as well.
This was the situation five years ago, integrating the battery into the car was time consuming and expensive. But this is not the case anymore. The MEB platform from VW takes 8-12 battery packs. They showed the pack compatible with 3 different cell configuration already, 2 pouch cell, and a prismatic cell, different manufacturers. It is just a standard square box, so you only need to integrate the battery into the box, which then can go into dozens of different cars. For a range of cars, starting from a hatchback, ending with an SUV. If someone leapfrogs the others in battery technology, integrate into the box, done. Probably you can fit a Tesla cell into the box, if they decide to sell the battery.
And that's just VW, Kia has their EV platform ready, and Nissan and Toyota is working on it. By not betting on a single technology, you have the possibility to adopt your car faster.