Lattice does not apply to all meshs?

Hello,

I try to modify a floor with modeling mode > deform > lattice but without success, the tool works for other meshs but not this one and every box I create.

The floor is just a box, a staticmeshactor, do I miss an important info on the lattice tool?

Thank you,

https://youtu.be/ejWBchGr6-4?t=392 TimeStamped