I'm pretty sure that the games of the era were simply reflecting popular culture in terms of favorite leisure time activities as well as movies & TV shows.
I grew up in Michigan in the 60's, and I can tell you that bowling and pool were very popular activities and 'card nights' were popular with people of all ages (not just poker but euchre, gin rummy, etc.).
If you look at the popularity of Westerns on TV it's not surprise that there were also so many Western themed pinball games. Even my favorite pinball back glass - Sing Along - presents the popular (at the time) activity of Caroling during the holidays.
This "art" imitating life phenomenon is yet another reason why I love EM games - particularly those from the 60's.