Marketing is the way manufactures sell rods
If they didn't push the latest thing, everyone would just keep fishin' the 'latest thing' that they bought two years ago
Or 10 years ago
Or 25 years ago
Rods don't suddenly become obsolete
That said, I'm thinking about building myself a 7' 9wt for fishing saltwater from my kayak.
It's a matter of landing fish easier rather than a casting thing