Non muslims are allowed to enter saudi arabia but theyre not allowed to enter mecca where the pilgrimage is taking place because it's such a busy place because muslims from all around the world travel there to carry out their religious duties. Theres already so many people travelling there and only a certain amount of muslims can go there. Going to mecca is compulsory for muslims as part of their faith. This is why non muslims aren't allowed to enter. If non muslims were allowed to enter mecca this would restrict the amount of muslims that were able to go there.