That was very restrictive visa.
Only 500 could be issued a year and the number of qualifying hospitals who could sponsor it was very low (about 14 according to Wikipedia).
The validity was for 3 years, non-renewable and once held, the person could never apply for it again.
Most adjustments would be from H1B for specialty nurses, but the vast majority of Filipino nurses in the past were RN who used Consular Processing.
There certainly was a period where EB3 was quite heavily retrogressed for Philippines and many probably abandoned, while others just waited it out. With relatively low wait times currently, I don't see any reason why the numbers would lower, especially as many have become wiser about qualifying at at least the BSN level which allows use of the H1B visa.