Oh Asher, you are a thinker! 😊

a mind too busy with thoughts and no space to take on new ideas?

This could be the case of individuals who rate high on neuroticism (one of the Big Five personality traits), or ruminators.

Are they not expecting the person in front of them to heed their words?

This might apply to people who are frightened to get in touch with themselves; being listened to, perhaps, makes their anxious, intrusive thoughts even louder.

What is causing this phenomenon I wonder?

From a more generic perspective, I believe that, people don't know what it is like to be listened to Asher. Imagine someone from their childhood years to their adulthood. How many times in their household, school and relationships proper communication takes place? Not most of the time.

Sadly, I am convinced this is the reality of most people. Back in the day, people had their neighbor from down the road, the best friend from school who still lives in the same town, the priest and so on. As these values and social structures change many other things get lost in the process :/ including the fundamental skills to establish proper communication.