Why most Nostr apps for mobile is slow?

The short answer:

- Background Processing.

Somewhat Long answer:

The nostr clients are fetching some events in background, Neither they are necessary or not, even they somewhat did not open the tab of where things was already rendered in background.

For example, The "Livestream" section.

You may not open it, But your client still tries to get events & renders stuffs for that tab in background.