Did you consider this in the plans and accept/know that some would not be able to or would choose not to attend?
Obviously at most weddings some invited guests will have to travel simply by virtue of the fact that friends and family can be far flung. However, I'm invited to one where (almost?) everyone will have to travel c. 5 hours. The B&G and most of their friends and families are SE based, the wedding is in Cornwall. So we have travel costs and accommodation on top of all the usual cost of attending, plus at least one day off work, and a really long journey, the kind you'd usually only make for a week or more.
There's no particular link that makes Cornwall important to the couple but it is a stunning location for a wedding, which is the reason for the choice.
I know attending isn't compulsory, but IME people do take offence if you decline!