SQL Server 2017 Always-ON
The exact similar question was asked on new Microsoft Q and A Site. I created a 2 node WSFC with AG configured for SQL Server databases. To simply put WSFC did not initiated a failover because the parameter Failure-Condition Level is default 3. And as per Microsoft official document Configure a flexible automatic failover policy for an Always On availability group for a SQL Server restart to trigger a failover you need Failure-Condition Level=1
This can be changed via Powershell, TSQL or from cluster GUI. One below shows value in cluster GUI