The IAAF is going from 16 events to 12 on the Diamond League circuit next year and the 200, steeple, discus, and triple jump all got the axe.
The IAAF says that the steeple and 200 will each be contested at 10 DL events next year (5 men, 5 women), and the discus and TJ will be at 2 (1 men, 1 women), but none of them will be held at the DL finals.
"Representative online research carried out in China, France, South Africa and the USA; post event surveys in Belgium, Great Britain and Switzerland and click-throughs on Diamond League social media videos during 2019 helped guide the Diamond League General Assembly, made up of all Meeting Directors, to decide which disciplines will be part of 2020 season. (See below)
"As a result of the research, and the decision taken earlier in the year that only 24 disciplines (12 male / 12 female) will form the core disciplines at all meetings, eight disciplines (4 male and 4 female) will not be contested during the 2020 Diamond League season. These disciplines are the discus throw, triple jump and 3000m steeplechase --three events that currently sit towards the bottom of the research conducted-- and the 200m which DL organisers felt would be too congested alongside the 100m, particularly in an Olympic Games’ year."
More details here:
https://www.iaaf.org/news/press-release/diamond-league-disciplines-2020