I remember that feature. Out of my, like 20 to 30 tries, it literally worked only once. I told about that feature to my friends too but they said that it wasn't working either.
So it was really not working at an acceptable level, or both me and my friends are terrible hummers.
I worked there from 2012 for 5 years. The query by humming was pretty amazing to me which is why I joined. And I'm pretty terrible at humming... Unfortunately though the database wasn't as extensive as the direct music match database. Perhaps you were trying songs that weren't included?
Fun anecdote: I witnessed one user sing a song into SH so pitch perfect that (from the results) it had made a direct music match!
We often heard that Google were attempting to replicate this technology. They even hired key employees involved in this part of the app. Still we maintained that particular technical moat for 12 years!
So it was really not working at an acceptable level, or both me and my friends are terrible hummers.