Several items missing from Share button in Safari on iMac but exist on iPad

On my iPad when I'm in Safari and want to send a web page, I tap the Share button and have many options such as Mail and Messages of course, but also Facebook, Twitter, Messenger, Instagram. I just got an iMac and when I do the same thing from Safari none of those latter options for the four social media apps appear in the Share menu and can't be added through the 'More' menu. Just to be sure, I went into the Apple menu > System Preferences > Extensions > Share Menu and they don't exist there. Why would there be a difference between iPadOS and MacOS for this?

UPDATE: I guess I've partially answered my own question. I've just read on the web that a few years ago Apple removed social app integration on the Share menu because of security concerns. But I'm not sure why that integration is available on iPadOS and iOS but not MacOS.