"But the resistance has decreased over the years."

This means its resistance decreases as the current through the tube increases.

The electrical resistance of a metal decreases as its temperature drops.

The resistance decreases because of the increased number of conducting pathways.

The current has increased, therefore the resistance must have decreased.

When the current doesn't have to pass through as great a length, the resistance decreases.

The resistance of a given material will increase with the length, but decrease with increasing cross-sectional area.

The law rests on an a priori assumption that a person's resistance to death decreases as his years increase.

Depending on the type of sensor the resistance will either increase or decrease.

Now as metals become warmer, their resistance to further plastic deformation decreases.