I think it's more cultural than anything else. SQL, despite being declarative itself, has a more imperative feel to it for some people (recursion being at the fringes of its standard) and people seem to believe more declarative means slower and more difficult to comprehend. The former is true only due to the implementation effort that went into SQL engines and the latter is plain false.
It probably doesn't help that the standard presentation of Datalog looks very much like Prolog, which most people think is an esoteric and failed programming language.
As for its limitations, it's disciplined in a number of ways, but those are features rather than shortcomings. So you can see in the post that it employs syntactic restrictions to ensure domain independence, it doesn't allow function symbols to have termination. It requires predicates that are not purely logical (extralogical) to satisfy certain conditions for safe execution. These make sure that your queries are well-behaved even before you start running the query. There is research on relaxing these restrictions (cough my work cough) without compromising on the nice properties that come along with it.
The nice thing is of course that if you want to do the same for SQL you start with pandora's box open and try to contain the chaos inside again, while with Datalog you're carefully trying to make the best out of it without unleashing madness. The latter is a much nicer foundation.
It probably doesn't help that the standard presentation of Datalog looks very much like Prolog, which most people think is an esoteric and failed programming language.
As for its limitations, it's disciplined in a number of ways, but those are features rather than shortcomings. So you can see in the post that it employs syntactic restrictions to ensure domain independence, it doesn't allow function symbols to have termination. It requires predicates that are not purely logical (extralogical) to satisfy certain conditions for safe execution. These make sure that your queries are well-behaved even before you start running the query. There is research on relaxing these restrictions (cough my work cough) without compromising on the nice properties that come along with it.
The nice thing is of course that if you want to do the same for SQL you start with pandora's box open and try to contain the chaos inside again, while with Datalog you're carefully trying to make the best out of it without unleashing madness. The latter is a much nicer foundation.