Ilm-history system index does not start with a dot

Hi

Here are the typical system indices found when using the Elastic Stack 7.6 (ES and Kibana are relevant here):

GET _cat/indices?h=i&s=i
.apm-agent-configuration
.kibana_1
.kibana_task_manager_1
.monitoring-alerts-7
.monitoring-es-7-2020.06.30
.monitoring-kibana-7-2020.06.30
.security-7
.triggered_watches
.watcher-history-10-2020.06.30
.watches
ilm-history-1-000001

I am wondering why ilm-history is not declared as a system index (which by convention start with a dot). For me, ilm-history feels very similar to .watcher-history for example. Am I missing something?