It is the process that, IMHO, started much earlier, and you can date even to advent of television in 1950s and, undoubtedly, to introduction of home video in 1970s and 1980s.
The current standard of 80-120 minute feature film was actually established roughly a century ago, and had more to do with economy, ticket prices, time an average filmgoer could afford to be in cinema etc. than actual technology and culture.
Even before, longer films were something of a special cinema events reserved for most epic and most talked about films. Or very niche arthouse dramas.
Posted using CineTV
Every society has the kind of cinema it deserves. Happy to be enjoying what is (still) good anyway.