Some butt hooks may touch the ground if the prone was HFT prone. If it's proper prone with the shooter resting on elbows
then the shoulder, and buttpad/hook, will be well clear of the ground.
The option is there for people to shoot prone in FT ... no one does. Why would they?
Lying in the mud ... having to get up and down ( average age of FT shooters isn't young ) ... needing the flexibility and strength in neck/back muscles ( average age of FT shooters isn't young ) ... having to learn how to use a sling and have problems with targets at different heights ( try proper prone on a target that is 15 feet up a tree ).
As opposed to ... sitting on a padded bag in a position that means most can shoot under an inch at 50m, and the better shots can half that, with some practice. So the sitting position is accurate enough, and far more comfortable, compared with all the disadvantages of proper prone.