I think you’re vastly overestimating the damage possible from the explosive payload a tiny quadcopter can carry, unless your goal is strictly terrorism i.e. intentionally targeting civilians.
Civilians dying as collateral damage during an attack/assignation of a legitimate military target is one thing, targeting civilians is another.
And before you say Russia does, don’t forget that Ukraine is dependent upon continued Western support, which is already fragile. It’s doubtful that support would survive them explicitly targeting civilians with suicide drones deep inside Russia.