At the AICPA's Practice Symposium/Tech+ Conference last week, it was revealed that the biggest concern for small accounting firms is staff retention. This might befuddle some since the enrollment and graduation numbers of accounting majors have been growing for years. But really, it's not that complicated.
Both experienced and new accountants have options and "work for a small accounting firm that is running on a dying business model" is one of the least attractive options available. Also, the "up or out" career path does not work for 98% of the people out there.
I honestly don't believe it's much more complicated than that. You're free to disagree of course; just be sure to include an explanation for why people like working at your firm. There are lots of firms out there that will want in on your secret.