It just boggles my mind that they haven't done it already. More niche browsers had official sidebar tabs ages ago, and so have Firefox add-ons (but as mentioned

It just boggles my mind that they haven't done it already. More niche browsers had official sidebar tabs ages ago, and so have Firefox add-ons (but as mentioned it's become a huge pain to set this up properly). But beaten to the punch by Edge? Someone must have made a decision 10-15 years ago that this was a "power user" feature and with their sliding market share it wasn't worth chasing that small segment of users. But then who are they trying to get as new users? Or maybe they figured having add-ons like Tree Style Tabs was sufficient, and don't care that no normal person will be able to hide the top tab bar and set it up as a proper UI. But again, less customizable than Edge isn't a great look.