Question

why were every elections won by PRI in Mexico

Answer 1

The Politics of Mexico take place in a framework of a federal presidential representative democratic republic whose government is based on a congressional system, whereby the President of Mexico is both head of state and head of government, and of a multi-party system. The federal government represents the United Mexican States and is divided into three branches: executive, legislative and judicial, as established by the Political Constitution of the United Mexican States, published in 1917. The constituent states of the federation must also have a republican form of government based on a congressional system as established by their respective constitutions.

Answer 2

Every election won by the party called PRI in Mexico because :
(1) Until 2000, every election was won by the dominant party called PRI.
(ii)  In its presence, opposition parties did contest elections but never managed to win.
(iii) The PRI was known to use many dirty tricks to win elections.
(iv)  All those who were employed in government offices had to attend its party meetings.
(v)   Teachers of government schools used to force parents to vote for the PRI.
(vi)  Media largely ignored the activities of opposition political parties except to criticise them.
(vii) Sometimes the polling booths were shifted from one place to another in the last minute, which made it difficult for people to cast their votes.
(viii) The PRI spent the large sum of money in the campaign for its candidates.