Since his death, many Chinese have found themselves being prevented from publicly remembering their former leader. Several mourners are reported to have been beaten by police.

The only large-scale memorial events have been held outside mainland China.

Why is the words 'large scale' have written with a hyphen? I wouldn't write 'large-scale'. In the above it is an adjective.
You have answered your own question: it is hyphenated because it is an adjective.

Large-scale operations in Iraq began eight months ago. ADJECTIVE
The operations in Iraq are on a large scale. NOUN
Thanks Micawber. I would look this point up in grammars.