Call me a tin foil hat conspiracy theorist if you must, but I think Nintendo intentionally made too few because they didn't want people to buy them. Instead, I think the whole thing was a viral marketing ploy for their Switch. They don't make enough but remind the gaming public how much they like (liked) Nintendo.
Call me a cynic ... but I think very differently.
I think that the Switch wasn't going to be ready for Christmas, and they needed something to sell and keep them in the spotlight after the awful Wii-U debacle.
So they made as many NES Classics as they thought that they could sell, and they were surprised by the demand.
Now that the Switch is out and getting positive response, they want that to be their talked-about-and-purchased system over the Summer, and into the Christmas run up, with no distractions from anything else.
Did anymore see the press release?
"Throughout April, NOA territories will receive the last shipments of Nintendo Entertainment System: NES Classic Edition systems
for this year."
Now that Nintendo are sure that their fanbase will lap these up, I fully-expect that there
will be an "NES Classic II" next year, or the year-after, when the Switch has cemented or failed-to-cement its place in customer's hearts.
Then exactly-the-same collectards will go out and buy that, and
maybe they'll make enough-extra for everyone else.