It most likely has damaged roots because they got too dry. Dry roots die and wet roots rot, so it is mandatory that you have good drainage to keep the roots from staying wet and a good mulch to try to keep them from getting too dry and also to keep them cool.

One cause other than not watering, is improper planting. Here is what rhododendron and azalea guru Harold Greer of Greer Gardens in Eugene, OR, said:

"Quite often a plant will get completely dry and then no matter how much water you apply, the rootball will just keep shedding it. The top of the soil may seem wet, and the soil around the plant may even be very wet, but the actual rootball of the plant is bone dry. This is especially true for newly planted rhododendrons, and it is the major reason for failure, or at least less than great success with that new plant. It is hard to believe that a plant can be within mere inches of a sprinkler that has been running for hours and still be dry, yet it can be SO TRUE!"

This is caused by not opening up and spreading out the roots before planting and then thoroughly soaking the soil after planting.

You might dig it up and make sure that the root ball is not dry. Then replant with the roots properly spread out and lots of drainage. That may mean using a raised bed. Never let the roots dry out when planting or transplanting. It doesn't hurt to dip them in muddy water before planting.

It is best to water deeply once in a while rather than watering a lightly all the time. I try to check my new plants once a week or a week after any decent rain.

Here is a link that might be useful: Planting azalea

I forgot to mention that this Satsuki is potted. The soil it had wasn't draining very well at all, so I switched it's soil to one that would drain much better. The roots looked and felt healthy to me (assuming rotting roots smell weird or feel funny- I wasn't 100% sure of what to look for) and I believe the center of the root ball was getting wet. I'm really hoping that it just needed a different type of soil.