Anki runs on desktop: you have to be chained to a desk rather than taking advantage of idle moments when you are on-the-go. Even if you have it on a laptop, you still need a place to sit; SRS on mobile can be used anywhere, like standing-room-only public transit.
The AnkiMobile companion app for iOS is a paid app that is somehow chained to the desktop version, whereas AnkiDroid is a full-featured clone of Anki that you could use air gapped without ever syncing anything to or from another device. It has integrated management of decks and note creation/editing.
Every other SRS app out there is just playing very distant catch-up to Anki/AnkiDroid. They usually mention Anki in their pitch, trying desperately to explain why some very minor and very subjective negative point about Anki is worth switching to their massively inconvenient solution.