Of course the underlying storage can be (and often is) a bunch of specially prepared relational tables.
But the strength in graph databases comes from restating the problem in different way, with query languages targeting the specific problem space.
Similarly there are tasks where SQL will be plainly better.
The SQL standard now includes syntactic sugar for 'Property Graph Query'. Implementations are still in the works AIUI, but can be expected in the reasonably near future.
And for efficient implementation the database underneath still needs to have extended graph support (in fact, I find it hilarious that Oracle seems to be spearheading it, as they have previously canceled their graph support around 2012 - enough that I wrote about how it was deprecated and removed from support in my thesis in 2014.