Earlier quoted context omitted.
First of all, these are integrations that you explicitly install (like installing an app), so that's obviously opt-in. That's a bit different from the adtech stuff many companies do without any benefit to you. Second, why do you ask just about Google and not the other companies involved? For example, if you're interested in the Trello integration, you also need to trust Trello with any data you send there. Presumably…
Opt in isn't enough to stop it becoming a toilet. Years of Britney Spears Naked Screensavers and malware "removers" have taught us that users are idiots. You can net a bazillion users with one "unlimited space" add-on. Obviously, there's some vetting but that doesn't always work. These add-ons could run on Google's servers and only have connectivity to your inbox and session. Instead, this appears to allow companies…
They seem to be part of "GSuite Marketplace," which is what businesses use, so presumably the domain admin would also have control over which apps can be installed.