Adversarial App Store policies blocking key/core features like zapping notes and content directly. There are workarounds that tech savvy users will use, but most people will use whatever is available in their app stores.

Separately, the risk of some large and well-funded company creating proprietary features or apps that gain popularity due to better marketing, legal avenues, etc, and lock users in, rather than letting users take full advantage of the open nature of the network protocol. The portability of your identity is key to Nostr’s appeal, and anything that prohibits that portability is ultimately bad for users.