Stock not reviewing the trendy vectors?

Plan ahead. Stock customers purchase time sensitive/seasonal assets several months ahead of the target date. They need ample lead time for creation, revisions and client approval. 

Submit your seasonal assets 4-6 months ahead of the planned use date. 

I've had people download seasonal assets as far as 4 to 5 months in advance. And remember, there's always next year. A Memorial Day image that I uploaded last year finally sold this year.

Adobe Moderators don't know that your assets represent particular holidays or trends until they actually review them. So your premise that they're intentionally bypassing these close to the holiday is flawed. Nevertheless, seasonal assets that are approved just 10-15 days in advance of a holiday have already missed any design windows or deadlines for that holiday. 

So far as I/we are aware, it's mostly first in/first out when it comes to review.  So yes, if the review time is 6 weeks and you submit 4 weeks before a holiday, then you'll likely miss the holiday.  Planning ahead will be crucial for this.

But sales for a holiday probably happen ahead of time anyway, so getting assets approved 2 days before a holiday probably wouldn't net a ton of sales if I had to guess.  If I were a designer working on Christmas advertisements for instance, I'd probably be working on them in the Fall.