In the past I have been in between Cosmopolitan offers for a few weeks before they started to arrive again, especially if I currently have a upcoming trip scheduled with them. After the trip is taken then the offer or offers usually start arriving again 2 or 3 weeks after the trip. I doubt the offers have dried up completely unless during your last visit you put less then 4000 or 5000 points on your card a day, without factoring in the 2X or 3X you get for certain identity tiers or if you low play your April trip.
Marketing offers from all casino groups can be strange. I didn't low play Mandalay Bay/Delano last year but earlier this year my offer was crap, 2 comp nights with low free play and resort credit. Then today out of the blue a offer appears for $500 resort credit, free play and 3 comped nights and discounts on spa,show and cabana.
Go figure.