Because extension support wasn't considered ready for normal (non-developer) usage up until now, and this announcement you're commenting on literally starts with saying it's gonna be ready by the end of the year.
The irony is addons were natively supported by the regular version of Firefox for Android up until they made the Quantum update, when they removed them and only later with Nightly allowing them to return.
I used to have a number of addons installed at that time, including Stylish (prior to the hostile changes), uBlock Origin and UnMHT.
The Quantum update was an update to the Desktop version of Firefox that happened in 2017. Mozilla did not remove access to any mobile add-ons at that time.
You probably mean the Firefox Daylight release that happened in August 2020. Firefox Daylight or Fenix was a completely new browser, not an update. That completely new browser did not fully support add-ons at the time it was released, which is why Mozilla introduced the restricted list of "supported" add-ons. I'm not quite sure how this is ironic. You seem to think that Mozilla somehow did this to get one over on their users, but I can assure you that this isn't the case.
> The Quantum update was an update to the Desktop version of Firefox that happened in 2017. Mozilla did not remove access to any mobile add-ons at that time.
Legacy addon support was removed from Firefox for Android at that point, too. Wikipedia confirms that in 2017 v56 of the Android version was the last to support them[1][2] and according to the official Android release notes the update was also called Quantum.
You're apparently correct that it didn't technically remove support for WebExtension addons though the addons I used became incompatible with the switch (which unfortunately caused me to switch to another browser after a faithful period of sticking with Firefox), including most that never became re-compatible on either desktop or Android again, including the exceptional UnMHT and sadly Firefox since has lacked MHTML support to this day.
It seems the dropping of legacy addons similarly caused others in this thread to recollect FF for Android as having dropped addon support during that period, given the impact in functionality.
I used to have a number of addons installed at that time, including Stylish (prior to the hostile changes), uBlock Origin and UnMHT.