I think the answer is simple. If it was easy to advertise to the user other payment options, then what would stop developers from making free apps [0] that are unlocked in the developers website? Bypassing the Apple's cut.
I don't agree with this but I think it would be a good argument by Apple.
[0] Assuming that these free apps would be functional but very limited so they don't have the same problem as the Hey app.
I don't agree with this but I think it would be a good argument by Apple.
[0] Assuming that these free apps would be functional but very limited so they don't have the same problem as the Hey app.