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.
Interior door height off floor.
Interior door height off floor.
Figure 2 floor relative to entry door.
The standard i use is 1 2 over finish floors 3 4 is acceptable.
The international building code has established doorknob height between 34 and 48 inches above a finished floor.
On the inside of the entry door finished flooring is laid on the concrete or wood sub.
Installers typically drill the hole centered 36 inches above the floor if not specifically instructed to do so differently exceptions to the rule include doors that provide egress into swimming pools or other water features.
To fix the issue the doors need to be removed bottom of the jambs cut and reset the door.
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.
I have never seen a door set with that big of a gap unless it was to get past floors that were not level.
The standard height of the rough opening for a door is the door height plus 2 5 8 inches.
The height of common doors is 6 feet 8 inches.
The additional room allows for a 3 4 inch top jamb a shim.