because drug development is very hit and miss. Not every drug that makes it to Phase I makes it to Phase II, not every Phase II makes it to Phase III, and not every Phase III is approved for market (look at Azli, for example).
Plus, there is very little interest in CF drug development because there are only 70,000 of us world wide. Compare that to millions of heart disease, cancer or diabetes patients.
This is why fund raising is so important - donations incentivize drug companies and the CFF to develop CF drugs.
Check out this article: it explains why we're so fortunate to have the CFF's business model:
<a target=_blank class=ftalternatingbarlinklarge href="http://www.businessweek.com/technology/content/apr2008/tc2008042_241404.htm
">http://www.businessweek.com/te.../tc2008042_241404.htm
</a>
the CFF pipeline is pretty rich right now - but of course not all drugs will make it to market. but at least we have a much higher chance of new drugs reaching the market with this biz model.