I'm not sure about this, I may be exaggerating, but aren't all four apps you mentioned (Spotify, WhatsApp, AirBnB, Uber) built on Electron? So they'd be using SQLite in the Node portion as their storage. That's their "server side", not client side.

For that portion (the locally-run mobile backend - the middleware) I guess it would make more sense... so I see what you're saying.

[Edit: Of all 4 things - Maybe only Spotify is actually an Electron app...? Although I'm confused as to how the rest could leverage NodeJS locally]