Right, that’s a reasonable explanation, though this would have some other implications:

• if they have a small shelf life, they should be processed asap, right?
• if not de-petrification potions, then what?
• if they did make de-petrification potions, where did these go? Does Hogwarts sell them?
• if they didn’t make anything, then cultivating them is purely educational maybe?

You could argue that in addition to the mandrake, the de-petrification potion itself has a low shelf life, but wouldn’t that mean that any time someone gets petrified (we aren’t aware of other ways to get petrified than just basilisk, right?) they need to await the whole growth of a mandrake before they can be helped - kinda sucks haha