Sorry, I responded with private email in error, but replied more or less that perhaps because the Trump Charitable Foundation was never certified, and therefore could not legally solicit funds from others. Also, maybe they also lack any charitable works since buying self portraits would not qualify. I understand there were also payments received that might be construed as income, or in lieu of income, or something of the sort.
More the question of why it has taken so many years for an investigation, I think.