Are dynasty leagues supposed to trade year-round?

I'm new to dynasty and find it odd that my commish has had transactions of any kind - waivers, free agent pickups, AND trades - locked practically since the fantasy playoffs started in week 15.

Essentially, we are in a deep freeze until he fills the remaining seats, meaning about six months of the year (!) it's as if the league doesn't exist.

Sorry, but what defines a "dynasty" league? Is it merely that you carry your roster between seasons? Or is it also expected that picks, rookie hype, and NFL news flow can be traded nearly any month of the year?

I thought it was both of those things, maybe I'm wrong.