AP Style is technically a writing style guide for the Associated Press, or journalists, but it is widely used as a default arbiter of “professional writing.” For years, well since the internet was a big enough thing for AP Style to have an opinion about, the official AP Style rule for spelling internet was to capitalize it.
The idea, long ago, anyway, was that Internet was a proper noun. That is that internet wasn’t a generic thing, so much as it was the name of a thing. The difference between ship and USS Enterprise, for example. Linguistically, it isn’t necessarily inaccurate. Internet wasn’t a real word, before it was, if that makes any sense. So either, it had to be a name, or it had to be a fake, garlbedeegook word. As you can imagine, professional journalists do not use fake words.
Of course, most of the world moved on from that way of thinking a long time ago, but change comes hard to big, formal institutions, and the AP Stylebook insisted that you capitalize Internet whenever you wrote it.
There are/were also instances where you were supposed to capitalize Web, for the same reason, although, curiously, never website. Although until 2010, the official way to write website was as two words, with, yes, Web capitalized. As part of this same change, web never needs to be capitalized either.
This comes as good new to me, primarily because of the large number of clients who insist they want “AP Style” writing, but then keep sending my copy edit notes to no capitalize internet. I stopped fighting them long ago, but still from time to time, a more formal client wants the big I and going back and forth is kind of a pain because typing for a writer is a muscle memory thing more than anything else, so manually switching it up as you go isn’t as easy as you might think.
I’ve even written posts here before about how I felt the Associated Press Stylebook was making me look stupid by forcing me to tentatively capitalize internet before being told officially not to by a client.
Anyway, this is all effective, officially, June 1st when the newest edition of the Stylebook comes out and the words are there in black and white, but the world has already moved on. The speed at which this change was willingly embraced shows that it was probably overdue. But, better late than never, I guess.