I'd say the 1960s Civil Rights movement in the US was primarily successful because it mobilized the middle class.
I agree that that period was an outlier in terms of large-scale activism post-WW2. However, there was also the small matter of 50,000 dead draftees in Vietnam that propelled public anger. The US government had a vested interest in making policy changes that kept the peace, especially with the threat of an expansionist USSR on the horizon.
Isn't this true for middle classes in most countries? Would there be any tangible benefit if the Chinese middle class made a symbolic show of supporting human rights (as is often done in the west), while their leaders continued to use their tax yuan to prop up polluting industries, bad working conditions, Uighur mass detentions?