Boredom? Technology? Culture? Couldn't beat the high score?
In England it remained popular into the first third of the 17th century. James I/VI was a massive fan of the sport and jousts are recorded until the last year of his reign. Being involved in the sport was a good way to come to the royal attention, as the career of James' favourite Robert Carr, Earl of Somerset, shows. James successor, Charles I's entertainment interests tended towards drama, masques and collecting paintings, then there was nearly 20 years of civil war, instability and a revolutionary government which wasn't keen on any form of public entertainment (theatre, for instance, was banned). By 1660, when the monarchy returned, jousting was out of fashion.
It should be mentioned that jousting could be a pretty dangerous sport. Henry VIII got very badly injured doing it and got wounds that never really healed, and Henry II of France was killed (1559) in a jousting accident.
'Unnatural Murder' by Lady Anne Somerset (no relation) about Carr, his wife, his unsuccessful prime ministership and the Overbury murder scandal, is very good for a look at 17th century English jousting and court culture.