One of the axes this analysis seems to be missing is the subtle spectrum from "multi-word expressions" to "idioms". Traditional lexicographers have long published separate idioms books, such as the Merriam-Webster New World American Idioms Handbook and the Oxford Dictionary of Idioms.

Wiktionary doesn't need to make that distinction between MWEs and Idioms and tends to conflate MWEs and Idioms as there is no separate "Wikidiom". Arguably, that multi-book confusion runs deep on the internet because Urban Dictionary should probably be fully titled the Urban Dictionary of Idioms and Slang.

It's not just page limits but also categorical limits and classic lexicographers would build multiple books/volumes, not just settle on one "dictionary". Classic scholars would often have a "reference shelf" with multiple dictionaries, books of idioms, thesauri, and more. The CD-ROM and then the internet has kind of tunnel visioned that this entire shelf can be merely "one app".