But also remember that airline customers also opt for the more cramped and cheaper variants.

I long ago swore to pay for economy plus. It isn't much more and the space is nice. Enough people do that they still offer the this service

But also remember they do that because their employer has opted to pay them as little as possible

How far do you want to take this? :)

The thing is, this is far from universal. People don't buy a substantially worse smartphone or car to save $5. But they'll accept a substantially worse product to save $5 on airline tickets.

Which two airlines have substantially different products for a $5 difference?

If you didn't mean literally $5 perhaps you can give us some real examples of cost differences?

Personally I find so little difference between airlines in economy these days. And Premium Economy is nowhere close to a '$5' difference long haul these days

They don't, because competition erases those differences. It's a very competitive market. If people were willing to pay a little extra for a few more inches of seat pitch in economy, you'd have an airline that offered a few more inches of seat pitch in economy with slightly higher fares.

Well, we could always try communism just one more time.