Google’s addons are easy for the consumer to install and get the service running (typically just a couple of button clicks); however, by giving the application access to your Google services, you’re trusting that app to keep your private information exactly that … private!
Do you think all of these developers are trustworthy? Most probably are, but even if in the well-meaning group, addons get neglected and without someone to maintain them, hackers can leak your information.
Please understand that I’m not judging as I use a bunch of addons. They’re too useful and save me a bunch of time (specifically spreadsheet-driven addons like Autocrat and Power Tools). I try to remove addons that I’m no longer using and hope that my current set isn’t leaking my data.
By using Google Scripts, the developer does not have any access to personal data. I have no need for your personal data and am glad not to have the liability in trying to protect it. I’m simply a business owner (primarily in real estate) who’s sharing some cool tools he’s developed.