From previous answers, we know that Leomund's tiny hut (probably) has a floor, preventing enemies from burrowing into it from below. However, the spell also says that "creatures and objects within the dome when you cast this spell can move through it freely." This clearly allows such creatures to walk through the walls of the dome unimpeded. But by the same logic, if the ground fell out from under the floor of the hut, would the creatures inside still be able to stand on the floor, or would they fall through it just as easily as they can walk through the walls? Does the word "can" imply that passing through is optional, and a character interacting with the barrier chooses whether to collide with it or pass through? If passing through is an active choice, what about objects sitting on the floor, which cannot make any such choice?
Alternatively, if characters do not fall through the floor automatically, can they choose to do so if they want to? (For example, suppose they are surrounded and want to escape by burrowing underground, using the opaque walls of the hut to obscure their actions until the last second when the caster leaves.)
Best Answer
The use of the word "can" implies choice.
Any other time the word "can" appears in a ruling, it means that the thing is possible if you want.
Take the Combat rules for example:
All these things are optional. You do not have to move up to your speed, but you can if you want. You do not have to forgo moving or taking an action, but you can if you want.
Note that it does not say "If you want to interact with a second object, you can use your action, it says you need to use your action. This is because there is no choice, you must use your action.
Leomund was a smart guy
Given Leomund's history, I don't think he would leave such a glaring oversight in his spell. It would make the spell largely redundant, as you could simply remove the earth under the hut and the occupants would walk through.
As shown in this article by Nerdarchy, Leomund was a smart guy. I don't really believe he would design a spell like this with such a large flaw in its design.
I refuse to believe that such a clever and inventive Archmage would create a spell with such a simple flaw. I think he can design a working floor.
Conclusion
I would personally rule that the player can choose whether or not to pass through it, since the wording of the spell is in line with that and that would be best for my group. I also think it makes more logical sense if they are given the choice to pass through or not, since if you just passed through the bottom of the Hut, the floor is purposeless. There's no point to it if you have to phase through it and sit on the ground anyways.
TL;DR: Yes, they can pass through the floor if they want or they can choose to not pass through the floor and collide with it if they want.
However, I would also say that each DM should do whatever they think is the most fun for their group.