I don't know where you're staying, but I consistently get 4 pm. Have only ever been refused once, and that was during the height of covid and property (Essex House) blamed lack of housekeeping staff. Even at resort and convention properties, I've generally been successful getting late checkout, even though those properties are not required to provide (most recent was Mauna Kea, where they gave us 2 pm).
That's simply wrong. While there are reports of properties making that claim, it is absolutely not what the T&C say.