In some situations, a contractual dispute and a trespassing dispute should be kept separate. Say you hire a painter to paint the inside of your house. You refuse to pay, and so the painter says, “I’m not leaving until you pay me.” When the painter refuses to leave, you call the police and ask them to remove him because he is trespassing. The proper resolution is that the painter must leave but can sue you for breach of contract.
That may be so, but in that case, the painter’s refusal to leave is incidental to the object and purpose of the contract, which is to paint the house, not stay in your house.
In contrast, the object and purpose of the contract of carriage is, among other things, to require the airline to transport the passenger from location A to location B aboard aircraft C. Being on the aircraft is the whole point of the contract, and it specifically lists the situations when the airline may deny transport to a ticketed customer.