There are several advantages where I2P implementation is more suitable over Tor, e.g.

I2P is significantly faster when routing internal traffic, where Tor is optimized for low-bandwidth clients and high-bandwidth exit nodes,

I2P doesn't have floodfill routers hardcoded as Tor's directory of servers,

I2P is a packet-switched network (as opposed to circuit-switched) which makes it more rubust,

I2P supports UDP, Tor not,

in I2P all peers assist in running short-lived tunnels, not only client-only peers as in Tor,

I2P uses API to interact with the network directly, as opposed to SOCKS proxy in Tor,

I2P aims at being its own lower latency network.

Source: Why is Monero aiming to integrate I2P? at reddit