why is safari reader mode so limited?

it won’t let me click headers on wikipedia. it won’t let me view comment sections on ars technica or anywhere, really. it’s grayed out for some pages. i like it but i thought all this would be polished and better by now. what gives? is there any way to force it to work when it doesn’t on its own? and why does it want to become reader mode on shopping sites? that’s ridiculous and it needs a setting “not on shopping sites.” really, is there some way for me, the user, to improve it on my ipad?