Every application (or concept) can introduce “tabs”, but it means something wildly different for that particular application. Tabs (or instances) in an application immediately bumps into the concept of state (statefull vs stateless) in applications.

Sometimes, it makes perfect sense. The reason tabs made sense for web browsers since 2004 is because each web page could be thought of as a “stateless” instance of an application. You’re not asking for “tabs”, you wish every application could be “Stateless”. Stateless is a beautiful thing, until you understand what state is, and who needs to manage it.

If every “tab” of Spotify had no idea what the other “tab” is playing and you had to switch back and forth between tabs to pause-and-play songs, that would be a bug, not a feature. While 2 “windows” playing audio (if you instruct them to) is expected.