Ah, yes, it is definitely reasonable to draw that conclusion based on people's disinclination to spend 100% the fare for a 10% larger, somewhat less uncomfortable seat, and/or 1000% the fare for 50% more space and an actually comfortable seat.

You seem to have left out Premium Economy class that’s available on many (most?) airlines. Personally, I tend to opt for that fare class as I find the seat more tolerable at a reasonable price point.

Premium economy is still usually at least 2x the economy ticket price; on a long haul that will cost many hundreds to up to thousands extra.

What you’re probably thinking of is the US airline specific “comfort/extra/plus” add-on that is priced 10%-20% extra. There is a few more inches legroom but the seats are the same small economy seats.

The prices does not scale up too well for the travelers, but for the airlines. The extra that you get does not match the huge jump in price.

Premium economy / economy plus seem to scale pretty well. Most of the times I’ve booked it’s been about 10% extra in cost for about 10% space on the plane. E.g 34 inches instead of 31 inches of pitch.

To be clear, premium economy and economy+ are different things.

The former uses larger seats and is typically available on long-hauls. The seat is somewhat similar to old-style business class seats, or modern domestic first class seats. It is not priced at 10% extra, it is usually close to double.

The latter is priced at around 10% extra, but is the same old economy seat just with a couple of inches more legroom.

It would be nice to have to pay only 10% extra to get 10% more space, but the lack of scaling is by design on the airlines part, and textbook market segmentation.

Edit: this article has pictures showing the difference: https://www.cntraveler.com/story/whats-the-difference-betwee...

I once got an economy plus seat at a bulkhead and had to stow my laptop bag somewhere behind me. I'd rather squeeze into economy than pay extra for having no way to kill time but wonder whether it'll be stolen.