I mean, I've never seen it or heard anyone even mention it. It's that whole issue of ... it's not popular and it wasn't critically well received... so why put it on Toonami? It needs to at least have 1 of the 2 qualities. The plot summary on it in no way makes me think it would be a good idea.
BC, TG, Akame, Boruto, Naruto... they're not critically well respected but hey, they're popular. It makes sense to air them.
And I refuse to believe there's more than 10 people out there clamoring for more Lupin on Toonami.
Gridman may not even be a top 10 show this season but it at least found a way to get its name out there... through thicccc waifus =P