Why did Thomas Becket’s tomb become a major pilgrimage site?

Thomas Becket’s tomb became a major pilgrimage site primarily because of his status as a martyr for the Roman Catholic Church following his murder in Canterbury Cathedral on December 29, 1170.123

After his death, which occurred during a dispute with King Henry II over church rights, Becket was canonized by Pope Alexander III in 1173. The site of his death and his subsequent tomb drew large numbers of English and foreign pilgrims, which significantly increased the prestige and income of the cathedral. For nearly four centuries, his shrine remained one of the most famous in Europe, famously serving as the destination for the travelers in Geoffrey Chaucer’s The Canterbury Tales. The pilgrimage was also bolstered by the penance performed at the site by King Henry II in 1174.2345