Perhaps they offer more but I certainly note that the types of shops and local factors are much greater influencers of local availability than anything else.
For example, Medicare shops are offered almost exclusively 4th quarter. Tax shops are offered almost exclusively 1st quarter. Most of the rest of the shops I see are pretty steadily offered throughout the year on a weekly, monthly or quarterly basis.
Local influencers here that are seasonal are that many teachers mystery shop primarily during the summer and tourists, especially the RVers who may be here 3-6 months, do a lot of shops during tourist season.