When did bicycle chains go back to being bushingless?
There is a book written by Frank Berto titled The Dancing Chain - History and Development of the Derailleur Bicycle. The fourth edition was updated in 2012. On page 368-369 he discusses chain design and chain types. Apparently, the 1981 Sedisport chain was the first bushingless chain. Its main feature was that it shifted better than bush-roller chains and also better than the Shimano Uniglide introduced in 1976. At the time, I guess 5 gear sprockets were the rule. With increasing number of gears over time, the bushingless chain took over from that point.