> Myanmar, while spoken by fewer people than Yue, benefits from an official standard for romanization from its own government (not ISO)

Said standard getting ignored by most Burmese people in favor of ad-hoc romanizations, similar to Cantonese speakers in Hong Kong and Guangdong mostly ignoring various standards published by their respective governments.

> Jawi is a dialect of a language spoken by fewer than a thousand people total.

Malaysian Jawi https://en.wikipedia.org/wiki/Jawi_script is not a dialect, but an Arabic-derived writing system for Malay. While not all Malay speakers use it, it's certainly more than a few thousand.

> what international demand was there for a standard for romanizing Mandarin and why that is somehow not applicable to Yue?

Mandarin is an official language of the UN, whereas Yue isn't.