It's not about usage going up. It's about the cost of usage going up v the cost of operations going down.
As an example, if we are to trust this site (https://jcmit.net/diskprice.htm), a 2TB HDD was sold for about 160 dollars in 2012. You can purchase 8TB for 130 dollars now.
From this wikipedia article (https://en.wikipedia.org/wiki/Wikipedia:Statistics) we can see the amount of English articles has about doubled since then. Chances are that storage costs have not only not gone up, they have gone down.
As far as I can see, the text of Wikipedia is about 10GB. I don't know how much space the images occupy, but if we assume they take up roughly the same space, then a single 2TB disk would accomodate 1,000 Wikipedias.
Totally agreed that the cost isn't really storage, but I wanted to point out that you're underestimating a fair bit on the size. Conveniently, there's a wikipedia article about this: https://en.wikipedia.org/wiki/Wikipedia:Size_of_Wikipedia
"As of 21 September 2022, the size of the current version of all articles compressed is about 21.23 GB without media."
(Note that's gzipped, so the actual size is much higher in-use.)
Media is, of course, vastly larger. Sadly, the last number given was from 2014, so I'd expect it to have increased massively since then:
"The size of the media files in Wikimedia Commons, which includes the images, videos and other media used across all the language-specific Wikipedias was described as well over 23 TB near the end of 2014"
> (Note that's gzipped, so the actual size is much higher in-use.)
OK; I did a quick dig to see how big Wikipedia is, but you've dug deeper.
You can still stick the whole English Wikipedia on a single disk, probably with all linked media (I suspect that a lot of what's on Wikimedia isn't linked from Wikipedia articles). So the main cost issue is serving content to the network; and there are lots of server farms that would cheerfully do that for the love.
… But have they had to scale to a degree commensurate with the amount of money they are spending? Absolutely not. The "Wikipedia has cancer" article makes that point handily.
The 21-22 annual plan [1] just shows "Technical Infrastructure" as 23.8% of "Programmatic", which is 76% of the budget, so 23.8% * 76% = 18%, or $27m.
"Technical Infrastructure" includes "all the engineering and technology" though. I'm not sure if a breakdown which includes server costs is available? I remember it being a pretty small piece of previous budgets.
Internet hosting costs have long been stable at about $2.5 million. You'll find them on page 5 of the following pdf (the page is numbered 3 and headed "Consolidated Statements of Activities"):
Annual revenue was $163 million. Of course hosting costs alone don't cover the entire outlay, but Wikimedia's budget and money demands have absolutely exploded in recent years.
I'm pretty happy to wager real money that Wikipedia has had to scale significantly in the last ten years.
But, hey, if you've got evidence to the contrary, I'll happily read it.