Colston, no one is saying you have to buy a new rod.
I think the number of reasons could be infinite.
You break one.
You outgrow one and want to upgrade.
You want a different rod weight.
You want a faster action rod-
Or a slower action rod.
You want one for a back up, or the old one will become a back up.
Because you want one.
Because you can.
Just a few reasons.
And what about the newbies? The have to start with something.
Progress, I think is the key. They're just providing what people want (and maybe they are dictating what you should buy) And you have to admit they have a great product for most flyfishers.
It's almost like computers. But I'll be damned if I would work on a 386 with dial up these days.