(all imho)
Guess it is not used that much. In most scenarios you have to create a proper port-forwarding in your home-network or have a public IP on your mobile contract with a huge amount of traffic included. People doing/having/knowing this usually figure things out themselves…
Additionally a tor relay does not create this statistics you are talking about. It will only show you how much traffic was used and that’s it.
On the other hand, Snowflake works mostly out of the box and helps a lot of users in affected counties, so it’s reasonable to nudge people this way.
So with limited resources I hope the work on implementing webtunnel in Orbot is prioritized and not a nice to have feature…