Go to one of the several public ClickHouse endpoints and run this query:

  -- Elastic vs CH in a single table. 
  SELECT toYear(created_at) Year, 
         uniqIf(creator_user_login, repo_name in ('elastic/elasticsearch')) "Elastic", 
         uniqIf(creator_user_login, repo_name in ('yandex/ClickHouse', 'ClickHouse/ClickHouse')) "CLickHouse" 
  FROM github_events 
  WHERE event_type = 'PullRequestEvent'
  AND merged = 1
  AND repo_name in ('yandex/ClickHouse', 'ClickHouse/ClickHouse', 'elastic/elasticsearch')
  GROUP BY Year ORDER BY Year

You can access the ClickHouse web UI for this dataset here: https://github.demo.trial.altinity.cloud:8443/play?user=demo. The password is "demo" (type it in the left side.) This is the Altinity.Cloud copy of Alexey Milovidov's excellent github_events dataset.

When I run this query I get the following numbers.

  Year|Elastic|CLickHouse|
  ----|-------|----------|
  2015|    191|         0|
  2016|    299|        40|
  2017|    296|        85|
  2018|    284|       142|
  2019|    341|       232|
  2020|    339|       300|
  2021|    243|       294|

Just speculation on my part but the drop Elastic contributors may be a side effect of the licensing change.