This is only half true, and there was a good legal reason for it. I've read a number of books on pinball history over the last few months, and some authors offered a few interesting facts. Add-a-ball games were designed and manufactured to meet a specific need for "pocket" markets -- to get around local laws that outlawed "free game" tables. For some reason, getting an extra ball was not gambling, but being awarded a free game was. Go figure. Shows how misinformed lawmakers could be. Complicating this picture, the laws across the US were diverse: local counties and towns had their own laws, often different from their states and big cities. And they could and would change over time as officials changed. Merchants and distributors in those specific areas wanted a piece of the action and the income and traffic the pins would draw. For those unique markets, add-a-ball games were the perfect and only legal way they could get it. So yes, there lots much fewer add-a-balls made than the standard free game versions, but it had nothing to do with popularity. In those banned markets, they were extremely popular and just as fun to play. They just weren't plentiful. The manufacturers adapted: they wanted to satisfy a need and earn extra income. All they did was simply modify existing designs and production lines and stay tuned to changing laws.