Ignoring other issues, that means you're making the seats movable in significant ways, so they have to be engineered to take the loads of landing repeatedly for decades without breaking - that will probably increase the weight a lot (compare the construction of plastic bench seats in most buses, to the construction of long haul passenger buses.

Those seats are huge compared to airline seats. If you had that much space in the airline seat this wouldn't be nearly as necessary.

Dunno if it is still the case, but trains used to offer that as well.