I think Thierry Blancpain is spot-on. I've always published typefaces as soon as I was able to, with a couple of exceptions recently made recently where faces were released at specific type events, like Typographics (Space Mono in 2016, Spectral in 2017.) That's more about the event than the typeface
I would say that December and August, being summer and winter holiday months in the West, are obviously not ideal time to release anything that isn't specifically useful for either holiday. You see this in stuff like this graph of general interest in fonts on Google Search:
There is a steep drop at Christmas time, and there is a peak around valentines day (a lot of people need fonts to make their own romantic graphic designs, I guess and then this slides down to the July 4 summer holiday in the US, and then trends up to Thanksgiving, and then down to the Christmas drop again.
This is somewhat a different topic, but interestingly I've seen that, over the long term, it seems interest in fonts has trended down in the last 20 years. Here's the long view on Google Trends is from 2004 to today:
The longest view is provided by the Google Books n-gram search, where use of the word "fonts" exploded in the mid 80s (with DTP) and peaked in the early 1990s. The word "typefaces" traces a similar although more muted path (and in the above doesn't even register)