>>10909265they are generally not as sturdy as they want them to be for most age ranges unless you make them rather tall
getting them to "feel" and be fun to handle is a bit of a design challenge. Also fitting minifigures in is possible but a lot of finagling.
There's a lot of hair, hat and backpack pieces that make problems even worse. So just saying fuck it and sizing your figures way up or making it a singleseater is easier and more kidfriendly.