In my opinion that can be give it to 2 causes. 1st. Popup windows became such a commodity that users who where constantly annoyed by it tend to close it inmediatly, so shorter copy it's more easy to digest in that split-second before they close it, in that scenario the copy on the popups have been changing to a more call-to-action focus.
2nd. It has to be related to the adaptability (aka responsiveness) of the content, less text more easy to adapt and less time for the user to read.

tl:dr
Time and space, time and space...

If by any chance you are one of the few devs that can sleep, my advice is that to keep a notebook always near you during sleep hours, that way when you wake up write inmediatly the idea or ideas that get stuck in your head. I use that method and check my notebook after finishing a large project, then the hard part is to decide wich one is worth. :D

@ElectricCoffee take a look at Dynamicdrive, lots of headaches and hours lost there years ago for noobie me.

Just visited, still the same, but a great place if someone needs scripts for legacy browsers.

@Jamoyjamie sure, i agree with you in that it's quite good, with lots of useful resources.

I mean it is the most hated in the fact that someone took the time to create a Chrome extension just to avoid seen any of it. <(• ° •)>

To me is more like the designer is a confused puppy, and the dev is a vicious predator focusing on his prey.