[Ellie May]

The only thing I can think of is that's it's very tiny and the vet thinks it will take care of itself?

I agree with the above. Leaving it can cause the cauliflower appearance.
There are three ways to drain an aural hematoma.

Aspirate (just stick a needle in it (no anesthesia). They usually come back this way.

Teat Cannula - inserted while the thing drains. E-collar has to be worn for weeks. It's a relatively new method (it's my vet's method of choice). I'm not sure how it would work on a small dog like a Yorkie. Certainly worth asking about. Anesthesia not required, but I've never seen one placed in a tiny dog. I wonder if it would be too painful. So I suppose sedation may be needed. In this situation, if my vet was vonfortable putting one in a small dog (I don't see why not), then it's what I'd do.

Surgery - works very well. It's a lot to jump into the first time though.

It's okay to progress through all three and stop at the one that works. I'm not a huge fan of aspirating though since so many do come back. Might be a waste of $$$.

If you are concerned, then time for a second opinion.