When I developed Sid Sonic, this was one of my primary focuses. Our search capabilities and interface along with our design had to be user-friendly and easy enough for your mom to figure out. I think we accomplished this.
A big reason that searching is hard on most stock music websites has a lot to do with the metadata attached to the audio files. After we finish a studio mix on a track, we then move on to the metadata aspect of the track. Metadata is the organized text associated with an audio file such as title, description, tempo, genres, moods and instruments. This is not an easy process and one has to be very musical in order to accomplish this effectively. There are programs that claim to be able to analyze audio files and create this, but they are highly ineffective at this point.
Even when content creators upload music to various royalty-free sites, the sites owners usually don’t have control over how the music creators upload this type of data. The end result is that a lot of music is mis-categorized and generally not where it should be. There are no checks and balances in place to police individual content producers when they are uploading their content. This is another big reason Sid Sonic doesn’t license outside music.
Another thing that effects finding music is the search algorithms used within the design of the specific websites. Obviously some are better than others, but the more content a site has, the more vital it is to have a well designed search engine and accurate metadata. Again this is no easy task and issues get multiplied because of errors in uploaded content.
I think there are a few companies that are doing better at this and we like to think we are at the forefront.
As always, feel free to send in questions or comments.