Here's why:

* Argon makes up about 0.93% of the Earth's atmosphere, while helium only accounts for about 5.2 ppm (parts per million).

* Argon is a byproduct of the radioactive decay of potassium in the Earth's crust, making it relatively abundant.

* Helium, on the other hand, is much less abundant in the Earth's atmosphere. It is a light element that readily escapes into space, meaning its presence in the atmosphere is constantly replenished by radioactive decay and volcanic activity.

While helium is more abundant in the universe as a whole, argon is the more plentiful element in the Earth's atmosphere.