Avira> klal yisroel accepted on themselves to keep glatt in America (many in Europe did not), as part of strengthening kashrus
this is probably true, but if we define “klal israel” broadly to include various people who eat kosher but whom you may not necessarily respect, moev to glatt is probably due to marketing strategy of certifying agencies who want to have a broad standard accepted by stricter communities, I believe somewhere in the 80s, possibly also re-definig “glatt” to minimally acceptable, and even down to proverbial glatt chickens.