That's what you're hung up on?

see the other comments. pdflatex crashes when fancyqr is overworked, which I’ve seen happen when exceeding just 2 qr codes. There is also a typesetting problem w/big codes.

Even when it doesn’t crash the compiler, it’s very slow. None of the QR pkgs are sophisticated enough to store the computed result and reuse it from one compilation to another.

You would care in some situations. Someone needs codes to be scannable from a long distance: https://hachyderm.io/@dolanor/117079618531657267

I sometimes produce a document that is littered with codes. If the qrcodes are small enough, they can be in the doc close to where they are referenced. The bigger they are, the more intrusive they are to typeset around. If you are doing a bilingual doc with a different lang on either side of the QR code, It’s harder to manage a big code aesthetically. Then we are forced to consider moving all the QR codes to the last page in a references section -- which is a trade-off because it means the reader must track down the right code for the reference they want to follow.

QR encoding is computationally intensive. When I use the fancyqr package (which uses colors), I can only get away with 2 QR codes per document or latex crashes. (edit: not really a crash but probably terminates with → “ERROR: TeX capacity exceeded, sorry [input stack size=10000]”).

Consider artwork as well. A stained glass worker really needs to keep the labor of cutting glass to a minimum and has a strong incentive to have a reduced number of bits. But then it’d be a shame to do a lot of labor to get a stained glass QR code that yields all uppercase text.

So the poor decision to use all uppercase for the smaller charset impacts in several unpredictable ways. That is, you cannot predict all the circumstances that small QR codes are needed. But they could have predicated that all uppercase is less useful than all lowercase.