I don't think any of these are arcane puzzles for someone who wants a mathematical career, which is the target audience (see, 'likely one of the first irrational numbers you encountered in your mathematical career').
This is for undergraduate education. A 20 year old now was 6 years old when Minecraft came out. A 20 year old now studying math has very likely played a lot of Minecraft.
Also, the authors' respective institutions don't have a graduate level math program. Lynch's personal research is in combinatorics ("particularly connections between combinatorics and representation theory, topological combinatorics") and Weselcouch's is in "enumerative and algebraic combinatorics".
Rather than attribute it to "late-stage research boredom", why not interpret it as two young math professors (they are both in their 30s, I think) coming up with interesting ideas for their undergrad, math-interested students?
Because I believe that is what the ultimate aim of research is these days: to attract more young minds to eventually contribute to meaningless pursuits.
No need to turn that downerism into doomerism, or imply it's some sort of new thing.