It’s consistent.
The last time the convention really played a role was probably the 1976 Republican Convention where the incumbent Ford was chosen over the challenging Reagan.
Conventions are really a formality at this point. They used to decide the nominee, but that has changed. At the 1968 convention, Humphrey won the Democratic nomination without participating in any of the primaries. He didn’t need to compete against his challengers such as Eugene McCarthy, Bobby Kennedy (who was assassinated before the convention), and George McGovern. These candidates — all on an anti-war platform — had great popularity amongst the younger demographics. This, combined with Humphrey’s corrupt nomination, led to rioting outside of the 1968 Democratic Convention in Chicago. Hundreds of college students were beaten, leading to the prosecution and fame of the Chicago Seven and Abbie Hoffman. Humphrey and his running made Ed Muskie went on to lose to Nixon and Agnew.
After the clusterfuck that was 1968, the Democratic Party switched to the current primary system, awarding delegates based on votes in the primaries. The Republican Party quickly followed suit in 1972. Since then, the nominating convention has really only nominated the candidate once — the aforementioned 1976 Republican Convention.
Great question.