"Why cameras are banned on courtrooms? I remember the last US trial news all of them had sketches like this instead of photos and videos... "

In general, because the judiciary has watched what the "news media" has done to every other aspect of life, and doesn't want trials and judging to become a popularity contest.

They try to strike a balance by doing things like having most court of appeals release live or near-live audio versions of arguments, allowing tweeting from court rooms, whatever.

Just not the "let's put up the satellites and get nancy grace on live"