When a two sector duty becomes a three sector fuel-and-go, especially an overnight one, it is very easy to run out of hours in the event of a diversion. If you have held at destination for any appreciable time before diverting then the clock does not wait for you. Whilst I agree that it is better to run out of hours at your passengers' intended destination circumstances/weather may not be favourable.
If a crew has run out of hours the sooner they get to their beds, the sooner they can get their 12 hours legal rest and get back to operating again. TUI are not strangers to ACE, they have all the contacts for transport and hotels. OTOH they do aim to sell-out all their hotel rooms where they possibly can leaving little spare accomodation for an out-of-hours crew turning up unannounced. Legal rest begins when the crew-members get a room to sleep in. The problem is not as simple as you might think at first glance.
TUI's lack of communication? Virtually no airline directly employs aircraft or passenger handling staff away from their home base any more. Handling agents are employed under contract at pretty much all outstations. It is a cut-throat business and competition is fierce. If an aircraft turns up at your airport unannounced the movement is outside the contract and not catered for under your manpower plan. If it is after hours then you might be able to get the local TUI girl out of bed if you are really lucky but the handling agent does not have personnel on-call overnight to unload the aircraft or look after the passengers. Even when the early shift turn up they will be fully occupied with the planned movements for the morning. In any case..... How much enthusiasm do you think minimum wage buys?
This is where the airline industry is now. Customer service has been stripped to the bare minimum just like your supermarket or any online retailer. When it is going to plan it works fine. When it goes off the rails (as it so often does) then nothing is held in reserve to recover the situation. The mark of a good airline is how they look after and communicate with their passengers in time of disruption. I will leave you to allocate marks out of ten for TUI.