Clearly it isn't a gear issue.
It sounds to me like your group has no patience. We have wiped and wiped and wiped on boss fights but we go away, we think about it, we discuss it, we come back and we one shot it the week after. That's how we roll. It sounds to me like your group won't even think about what's going wrong, they give up and you end up having to find others and start from scratch. Raiding should not be an easy ride - it is meant to be difficult so you need to have a good chat with your team and see what's going on. If they are giving up because they don't feel like they are getting anywhere then this may be a fault of leadership and general knowledge of the fight - are you even attempting different strategies? Tonnes of different things could be going wrong here but without the commitment then unfortunately you won't get anywhere.