Taiwanese is another language... but let's use your simplified terms for now. Well, yes, pretty much this. It's not that different from writting "fish and chips" as "fish and fries" in British English.
Who’s mainly responsible for there to this day being no ISO standard for transliterating Cantonese, and its conspicuous absence from Google Translate (despite the whopping 86 million speakers—consider that Translate supports, say, Welsh, Basque, Dhivehi, and many others that are spoken by fewer than even one million), is probably obvious. That entity is much helped by the issue being opaque to most foreigners, who are sufficiently baffled by a completely different writing system to just not care and bundle all languages written in Chinese script into one basket.
Imagine a world in which Google Translate has one entry called “Latin” for anything using Latin script (Welsh, Irish, you name it) and another entry “Simplified Latin” for English.
There's no ISO standard because there's no actual standard. Even just within Hong Kong there are multiple systems in use.
It’s not as if there were no attempts to introduce a standardised way of transliterating Cantonese (like Pinyin for Mandarin) that got shot down by (you guessed it) mainland Chinese. They happen to have a lot of votes in relevant committees and consider this national interest as they try to maintain authority across a very diverse set of people speaking different languages.
Because otherwise the default explanation for why there's no ISO standard for Cantonese romanization is the same as why there's no ISO standard for romanizing Burmese, or Malaysian Jawi etc. There's little demand internationally for such a standard.
And if the Hong Kong government's standard, or the Guangdong government's standard (this one presumably preferred on the Mainland) is officially blessed by ISO, would people currently using something else really switch just because of ISO?
When saying “little demand internationally”, could you clarify what international demand was there for a standard for romanizing Mandarin and why that is somehow not applicable to Yue?
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.
Standard being ignored by laypeople doesn’t make it any less useful in formal contexts sensitive to ambiguity.
It's not a spoken language. It's only for written text.
> only in Taiwan?
Only in Hong Kong, Taiwan, and oversea Taiwanese/HK communities.