I think you are being unreasonable.They don't need to have the same interests and hobbies as you.
You are lucky if that is your main concern for your 18 and 20 year olds.
I would be far more concerned if they were hanging out in gangs causing a nuisance, getting driving, taking drugs, committing crime etc.
Are they happy and healthy?
Are they still in study or working etc?
If so I wouldn't be concerned about not wanting to ho on holidays, especially if you have taken them to visit different places.
Some children don't get the opportunity to travel, even if they want to ( health of them or family members, cist etc). Your child will have experienced visiting other countries where they have not.
They are still young. Their interests may change over time, and they may want to travel, but if not, does it matter providing they are happy.