Why does rye flour dough require more water? Most discussions I have seen on the internet recommend increasing water content when substituting wheat flour with rye flour.
I find this a bit puzzling since I always thought that hydration of the dough should be based on the protein content - more gluten means stronger dough, which means it stretches without tearing even at higher hydration.
Rye flour (at least the one I have) is very high in carbohydrates but low in protein content, so why is more water required?
You are correct that higher-protein flours are capable of absorbing more water.  However, protein is not the only thing that affects water absorption.  In addition, according to Bakerpedia, there are:

starches &amp; pentosans
enzymes
flour grind

Rye flour, while low in protein, is very high in water-absorbing pentosans.  Hence the need and ability to add more water.