While open-sourcing could help some AeroGardens maintain its value and better avoid becoming e-waste, there's also risk of the devices being hacked for alternative purposes that Scotts Miracle-Gro may not want to be associated with.
As if people don't hack proprietary firmwares with shitty security all the time? Do they not get that more often than not, it will be more secure if open sourced?
I think they don't do these things out of a fear of their stuff being exploited, they do it in case some time in the future they can somehow extract more profit out of it. They sit on it for decades like Nintendo and their 80s games or trade the IP and patents around from company to company.