vCenter may have turned off the SSH service.
On vSphere 7 you would log into vCenter, look at the settings for the host, under Configure > System > Services. If the SSH service is "Stopped", then start it. If you want the SSH service always enable, then edit the startup policy on the same web client page.
On vSphere 6.5, things may be a bit different to my description, but similar enough to get you to the right place. I my shaky memory serves me well, the services control is under Configure > System > Security Profile in vSphere 6.x.