It’s a good idea, some aircraft have quite complex fuel systems though so it would have to account for fuel moving between tanks.

E.g. the A330 has an inner tank in each wing (which itself can be split into two compartments if damaged), an outer tank in each wing and fuel in the horizontal stabiliser which is used for CG control in the cruise. All of that plumbing can leak too. You’d be adding significant weight and complexity implementing leak detection across all that.

Regardless of all of this, the aircraft is still fully controllable even with a total asymmetry (one side empty the other full) so balancing the tanks isn’t a massive priority.