I don't get why this isn't a feature for a long time yet

There is but needs to be enabled. Go to Settings > Chats > Voice message transcripts and turn the feature on

English, Spanish, Portuguese, Russian only

I'd wager that probably covers only ~30% of the world population, and considering that people who speak Mandarin for example use other apps, it probably covers an even larger slice of the Whatsapp userbase.

I think it is less than 20% of world population are native speakers and will receive audio messages in those languages.

On my iPhone I can choose from hundreds of languages

For transcribing WhatsApp audio messages?

Awesome, thanks!