As a google user, what... what am I doing ~~wrong~~ right?
Using a browser instead of the YouTube app?
Unless you're talking about Google links then yes. Amazon too, along with many other services. There's a ClearURLs Firefox add-on to remove them automatically.
But it's insidious with YouTube because people are much more likely to share YouTube videos on a public forum, and they just randomly started doing it one day.
User asked why they never see &si= on their links on Android. @Synnr said they may be copying the link from the browser, which suggests they don't even have the YouTube app installed, as it 'never happens to them.'