Sharding at table level is very complex and expensive. Fully give a single DB per tenant is very practical, and the reasons to do sharding (like reporting) is where you do the other fancy things (like ship events in to kafka, etc, etc).
Also, most issues of scalability are dominated by a few tenants that consume most resources, and distribute the loads is more easy per-tenant.
How do you manage that ?
Availability is kinda good: You could lose one/few tenants but that not take down all the rest (if they are isolated properly).
Is MUCH worse if all the db made the fancy way get down, or worse, you get a cascade of latency and/or crashed by the interlinked nature of the "scalable architecture that is fact share-everything global singleton".
And you can get a bit fancy (not done it myself, my customers tolerate a bit of downtime) of fork the tenant and upload it another node.