On the inside of the entry door finished flooring is laid on the concrete or wood sub.
Interior door height off floor.
The additional room allows for a 3 4 inch top jamb a shim.
Figure 2 floor relative to entry door.
The international building code has established doorknob height between 34 and 48 inches above a finished floor.
The standard i use is 1 2 over finish floors 3 4 is acceptable.
I have never seen a door set with that big of a gap unless it was to get past floors that were not level.
I just took a quick look at some of standards and regulations governing door undercut which is the distance between a door and finished floor as opposed to clearance which is door to sub floor.
The 2018 irc continues to require the bottom of openings created by operable windows to be a minimum height of 24 inches above the adjacent interior floor when they are more than 6 feet above the grade outside the window.
That is a lot of room for unlevel you have there.
The height of common doors is 6 feet 8 inches.
The standard height of the rough opening for a door is the door height plus 2 5 8 inches.
The awi gives no minimum but a maximum of over 3 4 is unacceptable.
To fix the issue the doors need to be removed bottom of the jambs cut and reset the door.