Google makes money from websites showing ads, so making a reader mode readily available would be counter to that. There used to be a hacky way to approximate reader mode in Chrome [1] but not sure if that still works. Just another reason to favor Firefox over Chrome IMO.
Google will always give only enough privacy options to give the veneer of supporting privacy, but never enough to truly allow it (e.g., anti-fingerprinting measures). You can't blame them really, it's just not their business model, but if you disagree with that model and its effects on you, you can choose a different browser.
I have seen it a few times, but only on mobile IIRC and it wasn't consistently shown across all pages where I wanted the functionality. I definitely can't seem to find it anywhere on desktop Chrome.
I think of extensions as a way to adapt the web to my preferences. Sane defaults are not that universal and it's good to harness the power of the web to make everyone happy.
Google will always give only enough privacy options to give the veneer of supporting privacy, but never enough to truly allow it (e.g., anti-fingerprinting measures). You can't blame them really, it's just not their business model, but if you disagree with that model and its effects on you, you can choose a different browser.
[1] https://www.cnet.com/how-to/how-to-enable-reader-mode-in-chr...