If my application is retrieving millions of rows, it may be because I need to pass a window function over millions of rows. Or it may be that I need to copy millions of rows from one place to another. Or I may need to compare them with other millions of rows from another source somewhere else. Or I may need to transform those millions of rows on my application because I can scale it better than the database...
Just because you didn't think of some valid usage for a feature, it doesn't mean that there isn't any.
> it may be because I need to pass a window function over millions of rows
Every major RDBMS supports window functions (even MySQL, though recent). Why would you bring remote data into a local process to do something the remote process can do with its own local data vastly more efficiently?
Probably related to why the database has millions and millions of rows in the first place. Maybe someone read about denormalization in "Super Webscale SQL!" and blew up a trivial database. Or they're hoovering up vast quantities of garbage data and running it through a BI tract to produce bullshit.
I worked at a company that bilked the government for vast sums of money by doing all this and charging them for the hardware. The guvvies knew what was going on, but their little empires were more important if they got a bigger budget, so they went along with it.
Oh, God forgive if a company actually has a few million sales it must account for, or if a government body actually wants to control and verify what it does. No it's all because of stupid webscale! developers, because nobody ever does anything that isn't a web or finance startup! Ever!
Just because you didn't think of some valid usage for a feature, it doesn't mean that there isn't any.