As others have pointed out, epoxy is heavier than other glues. It is very strong though and used for critical joints such as tail sections, landing gear blocks, joining wings and firewalls. It also works great on materials such as plywood, plastic, etc. where some glues may not do as well. For things like wing ribs, it is overkill. Yes it is strong but both CA and regular wood glue are stronger than the wood pieces being joined if done properly; they are more than adequate. It would also be a pain to constantly have to mix new epoxy. Once you make a batch, the clock is ticking. It will start to cure and harden in the cup before you know it.