In Mexico's tlatelolco massacre why were the demonstrations protesting?

Answer 1

The demonstrators were protesting for reasons that included a general dissatisfaction with the PRI (Industrial Revolutionary Party) regime and increasingly oppressive governmental actions (including the occupation of schools).

Answer 2

They were protesting the massive "investment" made by the Mexican government to pay for the 1968 Summer Olympics. Considering that Mexico was much poorer at the time, people were enraged by the fact that for such a sporting event, US $ 150 million (US $ 1 billion in today's terms) were funneled to such enterprise, while the rest of the country was plagued by several economic, political and social problems.