Businesses and products use pop-ups because ‘everybody else is doing it’, not because it works. It may work, sometimes, but it’s not a given.
For all the surface differentiation and flash, business marketing is remorselessly conformist. That’s why ‘everyone uses pop-ups’ or, actually, all of the things that Nick mentions (and more).
It’s the same motivation that drives Amazon suggestions and Google ads. “Oh hey, you looked at this thing once. I’ll relentlessly stick it in your face until you look at another thing.”
I want to say : “Amazon, you’re supposed to be this marvelously smart data-driven organization, so why do you think that when I purchased a screwdriver set, I was embarking on my exciting new hobby of collecting screwdrivers? Do humans behave that way in your world, because they don’t in mine!”
This isn’t a new thing, either, advertising has been this way since pretty much the beginning of advertising.
Businesses are reactive herd animals. When one moves in a new direction they all go thundering off in the same direction.
