There's multiple levels missing when you do it yourself. Usually they would do their best to sort things out. At the very least it was a single call to deal with the issue to someone who knew how to rebook flights, find new hotels, whatever, not you struggling to figure things out on your phone. For a full mistake, yes, they'd usually reimburse you, if not there are regulations around refunds and things like small claims court.

Doing it yourself? Good luck! Hope you've got good service on your phone where ever you happen to be when things go wrong.

They were in a position to notice and correct most mistakes near-immediately, or at least shortly after making it. For most other cases, apologies and/or reimbursements backed by insurance if needed, transparent to the customer. In self-service, all that is responsibility of the user, but it's all built on requests to third parties, so the user is not in a position to unilaterally fix a bad request.