WTH Addons have 2 different urls for web UI

Why are there two different urls for addon UIs? One from the addon’s info page “OPEN WEB UI” link, and a different one from the sidebar.
Not something that necessarily needs fixing, I’m just curious about this.
For example:

File editor

ESPHome

Studio Code Server

Zigbee2MQTT

Never noticed that before. Also interesting that the second links don’t work unless you have the checkbox on the addon selected to show in sidebar.