1975 Anything is five gallons or more.
You are really comparing something 38 years old to now?
The US is worried about water availiblity in coming years. Much of the well water is eons old, and we're pumping it out for our use, and it doesn't replenish. We're good for now, but we're draining the water tables in the Midwest.
Brazil, Russia, Canada, and China will have more in future years for manufacturing.
Since 1992, all new toilet bowls have been 1.6 gallons or less. It's been 21 years.