bitemporal does not mean 'including timestamps' and out of existing RDBMSes only the truly most expensive ones support some kind of temporal queries; I've checked out for a bit, but if there's any with native bitemporal support that'd be quite the news

Most graph databases I'm aware of require a server and aren't embedded into applications. Using datalog and applying it to graphs also more general and thus preferable than cypher which is still a niche specifically for graph databases.

Also "because they can" seems obligatory.

I feel you, I am completely lost with all new ''graph flavoured DB". I keep challenging those (with the help of Opus model ) and the answer is always the same "use progresql".