We (humans) are following the last thing that worked (imagine if we could do true gradient decent on the algorithm space).
Good question, and I'm interested to hear the other responses.
They're mostly easy grant money and are being gamed by entire research groups worldwide to be seen as effective on the published papers. State of academia...
I suspect that this is because we've actually got a much more complex supervised training task than average (10k classes, multilabel), leading to much better supervised embeddings, and rather more intense needs for generalization (new species, new microphones, new geographic areas) than 'yet more humans on the internet.'
Here's some recent-ish work: https://www.nature.com/articles/s41598-023-49989-z
We also run a yearly kaggle competition on birdsong recognition, called birdclef. Should be launching this year's edition this week, in fact!
Here's this year's competition, which will be a dead link for now: https://www.kaggle.com/competitions/birdclef-2024
And last year's: https://www.kaggle.com/competitions/birdclef-2023