I don’t think it’s a trend. The new terminals at SFO and DCA are all glass. Even the new terminal in TPE is glass.
I think there may be some other reason to block the windows. For example, at IAD they blocked a bunch of windows on the new terminal so that they could build the bridge to the commuter terminal.
It’s clear (pardon the pun) that airport designers are going out of there way to make larger, more open, more friendly terminals and glass is a key element in this.