It has definitely changed, I don’t know when, but it’s been like this for at least the last decade.
Though, in my experience (NB: I’m a software engineer, which is a notoriously lax field.) only what the piece of paper says has changed. Hell, most of my employee handbooks have claimed that “full time” is 50 hours a week. They get away with it because I’m classified as a “computer employee” (lol) and make more than $35k/year (super lol) which means my employment is exempted from minimum wage and overtime pay laws.
Nobody that I know actually works that consistently. Most people I know don’t even do 40. I do 9-5 (or 8:30-4:30 usually), I take breaks when I need them and nobody has ever complained to me about the amount I’m working.
My only guess for why it’s this way is that having that be the official working time means it’s easier to fire anyone for no reason because they’re not working their “contractually obligated” amount of time.
100%
I’m unfortunately in a state with even more vague and useless definition of who gets to be exempt than the federal definition.