There is no "should" except what the most influential majority believes is correct. Language naturally evolves all the time and that is a good and beautiful thing.

You may have a preference or think this historical norm is interesting, but please stop with the "should" talk, it is irritating, condescending, and incorrect.

This particular norm is especially "wrong" (heh) because the overwhelming social majority has already left it behind. Clinging to it just because some academic wrote a book claiming that was correct or because 100 years ago that phrasing was common is especially misguided since for most modern English speakers it isn't just a thing they forget sometimes, but actually sounds wrong and weird to them. By any sane understanding of language that makes them far more correct than you.

Just like the plural of breakdown is breaksdown, the plural or checkup is checksup and the plural of hard-on is hards-on.

Actually no, it shouldn't.

https://www.limlessons.com/en/blog_post/compound-nouns-deriv...

In this case, "off" is not a preposition, but "lay off" is a phrasal verb

No. "Layoff" is a real, full word. https://www.dictionary.com/browse/layoff

Similar: He delivered a knockout punch. He knocked him out.

For the people who are downvoting this, I believe the HN title was edited, and was originally something like "Microsoft layoffs 1000 people". (It's always a bit dangerous to comment on the submission title without saying what the title was at the time of the posting!)