I think if you asked bowlers why they bowled league, they answer was to win the league and make a profit. And by a profit, they mean cover their costs of lineage and prize fund paid during the league year.
Now, as we all know, lineage has probably doubled, tripled or more over the past 20 years. League fees and prize funds have not.
So in previous decades, you had a $15 league where $5 went to lineage and $10 went to the prize fund. Well in today's prices, that same league probably pays close to $10 in lineage. So the league fees would need to jump to $20 a week just to be at same level as they were in the previous decade.
However, you are now paying $5 more per week or approx $170 (34 weeks x $5) a season and getting back the exact same prize fund. Less bowlers are being profitable. More bowlers are losing money and eventually quitting.
The work leagues that existed in the 80's and 90's have gone away for the most part leaving fun leagues and money leagues, but the money leagues are going away as it is it harder and harder to make a profit. Thus the bowler loses interest.