The problem is that micro freerolls don't attract the kind of people that a poker site needs to survive.  If a site has, say, a 1BTC/wk promotional budget and puts that budget into running 6 chips worth of freerolls a day, the only people that that is going to attract are people like you who just said that you aren't interested in depositing on a site.  Now that's obviously fine for you as an individual, but for the poker site that's bad because they are never making any money. 

If, instead, the site puts that budget into deposit bonus', guaranteed tournaments, or funding a rake race promotion of some sort, they are more likely to attract players who will actually deposit money and play regularly, allowing the site to rake pots and start recouping start up costs.  These types of people are also more likely to leave bonus money on their accounts and play more.