Exposure isn't necessarily good for an app.
Users frequently _cost_ money. Ask anyone who has significantly scaled freemium services.
Exposure to lots of users who might not use your service can kill your business.
If your service is really that good or serves a real need, you would recognize these potential users and market to them _aggressively_. You would even raise significant capital to do so if you did not have it. Seeing the value in your product, VCs would invest in you.
Even if your product has no inherent costs to provide as a service after it is made, you scale the money and time that invested in it based on your expected reach/profit and your profit model has just been thoroughly fked by Apple.
This definitely applies to people who produce music too because the product you're releasing has a profitable shelf-life (except for unicorns, really) and artists release on a schedule that their market (and they personally) can support.
You put a certain amount of money and time into an album based on how many people it will reach and the likelihood and timeframe before you can put out another one. Some artists release every few years, some every year and some release multiple albums per year.
If Apple is giving away your album for 3 months and you release 4 albums a year, they may be giving away 1/4 of your yearly income...(Think of it like Big O and worry about your worst-case performance.)
Using revenue streams that you don't control is hazardous. Relying on them is outright dangerous. Using revenue streams that you don't control AND marketing streams that you don't control? Suicide.
Note: this is not an argument for whether you should pay for music or not...that's a topic too hot for HN.