Why do most construction workers choose merit shops?

The vast majority of construction workers in Massachusetts, New England and across the nation choose to work for merit shop employers.

83.5% of MA construction employees worked for open shops in 2020, according to unionstats.com. 

Question: If being in a union is such a great deal, why do most construction workers prefer open shops? 

 

Question: If union membership is such a great idea, why do unions need recruiters?