Some discussion on TEFL Twitter:

I agree that most grammar books simply present it as "Here's the rule, memorize it". The one book I've seen that attempts to give a pragmatic explanation for this rule is "The Grammar Book" by Celce-Murcia and Larsen-Freeman

— Joel Swagman (@JoelswagmanJoel) September 17, 2021

I'm afraid I can't summarize their explanation in a tweet, but it's very possible this book could be in your school library.

— Joel Swagman (@JoelswagmanJoel) September 17, 2021

A little while later, someone offered another answer:

Here's the relevant bit, Chapter 5 Rules and Reasons: pic.twitter.com/muuQ1qtVGu

— Neil Anderson 🇪🇺 🇪🇺 (@neilpma74) September 17, 2021

I said above that I couldn't summarize in a tweet, but... this is very similar to what Celce-Murcia and Larsen-Freeman say.

— Joel Swagman (@JoelswagmanJoel) September 17, 2021

...only later did I realize that I had missed that the above quote was attributed to Diane Larsen-Freeman. The same author I was referencing. So no wonder the explanation was the same.

For anyone interested, in my copy the relevant information is on pages 435 from The Grammar Book.