* information tends to be private and/or commercially sensitive, this severs the links that graph dbs are good at representing (and made the "node focused" SQL approach the ubiquitous model that it currently is)
* objects in typical schemas have many more attributes that relations. while you could model things RDF style where everything is a relation, it is not the most intuitive for people
* when the previous constraint does not apply (e.g. data from a centralized social network), it is typically not too hard to emulate an adequate graph structure on a Pareto 20/80 basis using an RDBMS
so graph dbs end up being optimal only for a niche of situations and probably not the impact that the people / investors involved in their development would be happy with
on the other hand the ginie is out of the bottle and the decades-long SQL monoculture seems to be coming to an end. but maybe what results is a relational database+ type thingy [0] rather than two disconnected paradigms
[0] https://postgresconf.org/conferences/2020/program/proposals/...