Hi Catherine,
Thanks so much for your message. Baggage allowance is also to account for the ground transportation while on holiday & why these can be different to the airline you are travelling with. There's more info in the essential info on the website:
Baggage Handling and Allowance: The baggage allowance for all our holidays is one piece of luggage/ suitcase – with the dimensions of 76cm x 58cm x 25cm (30” x 23” x 10”) maximum weight of 44lb (20kg) per person, plus one standard piece of hand luggage. Irrespective of individual airline allowances the above limits apply.
They are set taking account of our wider operational requirements including ground transportations, porterage, etc. To avoid any problems with our transportation providers, possible delays and inconvenience to you and your fellow travellers, please ensure these maximum baggage conditions are adhered to. You are responsible for the carriage and care of your luggage throughout your holiday except for such times as it may be in the hands of the airline, here in such circumstances the airline specific terms and conditions relating to the carriage of luggage apply or when porterage at a hotel on arrival and departure is included. We will not be held responsible for any delays and/or additional costs arising from any breach of the above luggage allowances.
I hope this helps to explain the allowances specified and wishing you a wonderful tour!
Best wishes,
Just You Customer Care