There's no trend here really.. Express Entry is a young program and each year has seen changes. So we can't conclude anything.
However in this particular case, Ontario last issued NOIs on July 12, August 1 and August 15. Between the three sets, there were a total of 4,393 NOIs issued. After this, these 4,393 candidates had to submit their applications to Ontario and they had to go through an assessment process which typically lasts 2-3 months. After this assessment, the candidates are issued an extra 600 points (this step is the 'nomination') and they get ITAs in the next express entry draw. The nominations started flooding in from the first draw in October and this led to a spike in the 600+ points candidates.
So these 4,393 NOIs in July and August have almost all been nominated now. There are still maybe 10-15% left who should get nominated before the next 2 EE draws.
This is why you hear people saying the effect of PNPs will minimize at the start of the year. The next set of NOIs are expected only by the middle of 2020. So from the January draw onwards, there should be significantly less 600+ points candidates in the pool.