Airlines don't want to have to commit to always using the same model of plane. It's pretty common they downsize the plane if not many tickets have sold or upsize if they're selling well. They also do swaps in case of mechanical failure or large delays.

It's the reason they won't let you get a seat reservation till near the flight date (since different planes might have differing seat layouts)

Taking away this flexibility could easily wipe out their entire margins.

> It's the reason they won't let you get a seat reservation till near the flight date (since different planes might have differing seat layouts)

I feel like I have been able to pick seats on all of my flights for the past 10+ years no matter how early I purchase the flight. There is always some language that the airline is not obligated to give you that seat.

Ryanair is special in many ways… one being they run a very standardised fleet, almost entirely 737-800s with 737-MAX on order.

They do, but from what I understand, they're not obliged to use the same aircraft (e.g. last minute swapping due to maintenance or other reasons).

The "funny" thing though is that they renamed it to 737-8

That was already its name. Boeing 737 Max was the programme, with the 373-7, -8 and -9 models, like before 737 NG with -300 and -400 models. It's just that now they're heavily emphasising only on the -7,-8,-9 and skip the "Max" part.

Are/where all the -7, -8, -9's affected by this problem or only specific models?

Yes, I believe all 737 MAX have MCAS.