Many sources site GRE as supporting broadcast/multicast and IPsec does not. Both GRE and IPsec are merely tunneling protocols. Therefore there is nothing inherent about tunneling protocols which prevents Multicast/Broadcast.
What is it specifically about IPsec that does not allow for Multicast/Broadcast traffic to flow through the tunnel?
By comparison, it might be also helpful to also answer: What is it specifically about GRE that does allow for Multicast/Broadcast?