The reasons for stop clustering (num_layers)

[SCULX]

Hello, Thank your excellent work, I appreciate the idea in the paper. When I read paper and check this code, I still couldn't solve one problem, which is following:
in the paper:

...and summarization continues until further clustering becomes infeasible...

I want to know how you handled 'until further clustering becomes infeasible', because I think stopping clustering is a very difficult problem, so I carefully checked the code and debugged it, and found the following key codes：

if len(node_list_current_layer) <= self.reduction_dimension + 1:
             self.num_layers = layer
             logging.info(
                    f"Stopping Layer construction: Cannot Create More Layers. Total Layers in tree: {layer}"
               )
             break

So why stop further building new layers under the condition of len (node_list_current_layer)<=self. reducion_dimension+1? I didn't find the reason in the paper, nor did I find the desired answer in the issues.
It would be great if there were some reference materials.