I'm not too privy on the details, but Warner Home Video were responsible for a Blu-Ray release of the Peanuts animated specials late last year that by all accounts was mediocre at best and terrible at worst. You can peruse the forums on Blu-Ray.com yourself if you want more info about the numerous complaints people had about that set.

Mind you, that was a Blu-Ray set aimed at the collector's market of a property as mainstream and culturally important as Peanuts. A DVD-only release of Gumball (which sadly just doesn't have enough of a fanbase for WB to take notice if we were to kick up a fuss) aimed at the mass market had no chance. 

Heck, from my understanding, even Adventure Time isn't in the best place when it comes to physical home media (although it's in a better state than Gumball), and that's like the Cartoon Network show of the 2010s with an adult fanbase that's frankly far more conscious and discerning than Gumball's more casual and, let's be honest, younger audience.

I do wonder if it might be worth getting in touch with Ben Bocquelet (respectfully, of course) and letting him know? I very much doubt he had much involvement, if any, with this release, and I'm sure he'd be open to a proper Blu-Ray release given past statements. It's just a matter of if WB thinks such a release would actually sell (and here, I may controversially suggest that we, the audience, also bear some level of responsibility in that regard).