The 20kg allowance is Monarch's limit on the weight you are able to carry and that limit is per person (regardless of how many bags you pay for). There are limits as to how much passengers can carry.
Unfortunately, the airline has to set a limit and 20kg is theirs. It is simply not possible to allow everyone to take a limitless amount of weight in their baggage. Some Monarch flights travel as far as Sharm el Sheikh in Egypt and to allow excess weight to all those who would like to take it is simply not possible due to weight restrictions. Unfortunately, the aircraft wouldn't make the full journey without having to refuel with a full plane of passengers and this additional weight onboard.
Granted you were likely not traveling here but there has to be a defined limit across all flights to make it easy to understand the restrictions in place.
However, I will point out that it is possible to achieve your 60kg for 2 people by each having the max 20kg and the max 10kg each you are allowed in the cabin.
Originally Posted by caaardiff
Same with Thomson, Thomas Cook and most airlines. You pay for the number of bags you want and get 20kgs FREE. Anything over 20kgs you pay the excess charges (preboook or more expensive at the airport)
caaardiff, I think you are confusing the 20kg that tour operators include as part of a package when you make a booking with them. Cosmos, Monarch's sister tour operator who use Monarch, does allow 20kg free of charge but it sounds to me like this was just a flight that was booked.