I doubt that many bowlers have quit altogether or reduced the number of leagues they bowl in because the shot is too easy. As another poster mentioned, our lives are not only more complicated these days, there is so much more to keep us occupied.
Almost everyone is on the Internet hours a day, there are many, many sports activities for young people, starting with "play dates" for youngsters up through numerous sports for teens. When I was a high schooler (many, many years ago) you could play basketball or football during the school year. Baseball in the summer, if you organized a team yourself and joined a league at the "Y".
Nobody played soccer, field hockey, rugby, tennis, volleyball, organized swimming etc. etc. Nowadays, we have thousands of sports being shown on TV, back during the bowling heydays, there were only three channels on TV and most of those were fuzzy, if you could get them at all.
With all of these activities available it is no wonder that bowling participation is down. Most other sports have bigger prizes (golf, for example), more sponsors and a broader following.
Not too difficult to figure it out.
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Never take a sleeping pill and a laxative on the same night.