This is nothing new and has been part of the DV program since its inception in 1990. There is most likely no way to tell how many DV applications are ultimately denied due to public charge issues. You may be able to find out by filing a FOIA request with the Department of State and USCIS. They surely keep statistics on the number of applications that are denied, though possibly not by specific reason for each visa category. All immigrant visas not allocated in a fiscal year are lost. They do not carry over from year to year. DV winners must enter the U.S. on or before September 30th of the fiscal year in which their visa was allocated or the visa automatically becomes void.
Many charitable organizations that sponsor refugees will provide assistance to DV winners to help satisfy these requirements.