I don't know as much about Catholics or Jews, but the impression I get is many of them describe themselves as occasional, whereas Mormons tend to be one or the other — either in or out.
I can only speak to my personal experience as an ex-Catholic. I think Catholicism was best described by former NYC Mayor Ed Koch when he referred to it as “a cafeteria plan religion.” We’d see some families in church twice a year at Christmas and Easter. There were people who went to weekday mass every evening. There were Sunday mass regulars who practice pre-marital sex, use condoms and believe homosexuality is not a mortal sin.
Growing up in that wide range of believers in the Church, it was a bit of a shock when I went to college and experienced the black and white orthodoxy of other religions during interfaith bible studies.
I think it’s easier to stay in the Catholic Church because of that prevalence of people who don’t follow all of the Vatican’s edicts but still consider themselves Catholics.
I believe outside the US, there are countries where Catholics are predominantly more devout. It opens up the question of whether an American would ever become pope. It’s only been 40 years since the first non-Italian Pope was elected.
I suspect the exodus of Catholics after the priest scandals has caused a concentration of the more devout. But its been over a decade since I left for good, so I lack intel on what a typical congregation is like today.