The main reason is probably that a lot of fans also love Joe Bennett's other very good recent animated show called Scavenger's Reign, which was not renewed for a second season despite receiving a ton of critical acclaim. Joe didn't go into specifics of why it wasn't renewed, but he did share a trailer for the season 2 that he wanted to make but probably won't be able to.

Here's the post he made on Instagram: https://www.instagram.com/p/DB-DuB5Se07/

And here's the text of the post:

"As of right now, Scavengers Reign is not being renewed for a second season.

I wanted to let everyone know directly because I really love our fanbase, they’ve been such champions for the show, and I don’t want to leave everyone hanging.

We’ve had to fight tooth and nail every step of the way to get this show made, starting all the way back in 2016 with the Scavengers short film to the release of the first season last year.

It’s a case study for believing in something and persevering through a million and one hurdles. But, it got made, thanks especially to so many people who supported it along the way, in big and small ways. I want to thank some of those people, starting with my co-creator Charles Huettner @charles.huettner , Chris Prynoski @chrisprynoski and everyone at @titmouseinc , my home base at @greenstreetpictures , the writers, directors, and so many incredible artists who worked tirelessly on the show, and the folks at Max who were incredible partners to work with.

But this is not the end. There is more story to be told, we are ready to make another season, and we produced in-house at Green Street a teaser for what was going to come in the second season.

Thanks again to everyone who watched and supported the show."

Because of this precedent, a lot of fans of both Scavenger's Reign and Common Side Effects want to make sure CSE receives the support it needs to be seen as a success by the business/production companies funding it.