Communication between planetary bodies in space, e.g. from the moon, or Mars, takes a long time and has many shortcomings, like line of sight requirements.

Communication with interplanetary spacecraft is often silent for stretches of time; only getting updates on certain days & times of the week.

Why is this enough to be acceptable for deep space exploration?

What are the challenges with improving this? So far it does't seem like a priority, so there must be some reasons why this is okay, can it be expressed in an answer?

I was thinking about repeaters, or store-and-forward schemes, are these possible?