Is your water softener positioned before or after the water heater? If it is positioned before the water heater, it may be there to protect the water heater from filling up with calcium deposits. When I had a house with very hard water from a deep well, I once had to replace the water heater after it accumulated enough calcium deposit debris to fill about 25% of its capacity. My non-expert impression is that water heaters in particular can load up with calcium faster than it would collect in other parts of your plumbing.
My current house has a Whirlpool water softener where the water enters the home, so it protects both the hot and cold sides of the plumbing. The instructions that came with the water softener say that in addition to salt, I should also run “water softener cleanser” through it once every 3 months, on a day when the salt level is low. After it has cycled once with the cleanser, I load it back up with salt. If I do not use the cleanser periodically, the softener works progressively less well, despite continuing to use salt. The cleanser is primarily phosphoric acid, and it is supposed to clean the resin beads in the filter. If I forget to use it, and the water gets really bad, I have had to treat and cycle the water softener a couple of times to get it working properly again.
When I was young, my parents had a Culligan water softener, and it also used a purple liquid cleanser in addition to the salt in order to keep it working properly.
Running a couple bottles of cleanser through your system would be pretty cheap and easy. It might be something to try before going to the trouble of replacing the resin bead media.