Manga Reading Apps

I've seen multiple rules like: "do not upload on ***" why is that?

Are the groups having negative experies with those sites? I think that shouldn't be the case since they'd be less popular without them

Are there any law breaking endangerments? Since they are publishing on a different site it's still illegal (just like reading)

Reasons i listed above may or may not be true so it'd be nice if someone confirmed or denied them

I have no intention to offend anyone i am genuinely curious
And im sorry for any mistakes im not native

Like I used to use it back in middle school but then it vanished

in light of mangarock closing, does anyone have any other apps for their phone for reading manga? i do like mangago, but i like having an app with a friendly user interface thats specifically for the phone.