You don't get Blesta do you? ModulesGarden did their addon like their WHM** module most of the features are in WHM** already except the FTP / SSL / Emails / Etc via the client area, ModulesGarden script also works around Softaculous and others that most billing systems won't have. I don't think blesta would do that, if anything they'd have the options when making a cPanel package, like other billing systems.
The marketplace is where most plugins from Blesta (License Managerment, Project Management, and other Blesta modules / Plugins) Plus developers / designers who make themes and plugins. They can sell their modules / products though the Blesta marketplace or release free products. There will be a Verified title which will be a paid service and Blesta will look though the code and ensure it's to Blesta's standards.
Blesta make money by people buying their software, monthly licenses / owned licenses / Lifetime licenses / renewals for support & updates / Extra Plugins & Modules / custom work / and more.
I do see your point though but Blesta isn't another HB.