I think they were referring to RAM or storage space rather than human fatigue or mental effort, although I'm not a native English speaker so I may be misinterpreting.

Indeed, there are many low-end smartphones that run out of storage space after one or two years even without installing anything, just with the automatic updates of the preinstalled apps (Facebook is a major offender here, why does their app grow more and more?). Being forced to install an app to use a service when you are in this situation is highly frustrating.

What year are we in? I've got a $200 phone with 128gb storage and 4gb ram. It will be a long time before I can max this out if at all.

Not everyone buys a new phone frequently, and not everyone can or will spend $200 on a smartphone without a second thought, especially at the global scale.

Smartphones are getting better and hopefully this problem will be irrelevant in a few years, but I still know plenty of people for whom it's still very real at the moment.

Sure, I was part of a startup designing apps for emerging markets and I understand the restrictions but I think these restrictions changed somewhat for phones bought from 2018 on. I just returned from 2 weeks in India and it was common to see people in the streets with ~$200 phones

Sub $100 phones rule the streets here in Nigeria. In those cases storage is very precious and limited.

The flip side is that people who can only afford sub $100 phones are not as valuable targets to develop apps for.