I see a bit of confusion about what is traditional and what is not. Let me see if I can explain how both rules (hosting of out-of-town guests, and hosting of the bridal-party and their spouses only) have roots in tradition.
I have posted over and over, that there is no such thing as “wedding etiquette”. Thoughtfulness and conformity to social norms of good behaviour are everyday obligations. What we are obliged to do at weddings is just the same (if generally more formal) than what we are obliged to do in non-wedding circumstances.
When people you know — friends, family or connexions — visit from out-of-town, good manners requires that you offer them hospitality. If you have house-space, you offer that: the best you have but with no expectation that you need to offer more than you have available. No matter how humble your “best” is (up to and including “nothing”) you never apologize or feel ashamed of offering it. If you have a well-run kitchen and can offer a meal or meals, you do that. Or if your kitchen’s capacity to produce meals is dubious, you offer to take your friends out to dinner. Or if you cannot afford that, you offer them guidance as to where the good hotels and restaurants are, and maybe invite them over for dessert or cocktails or tea. Or invite them over to sit on the floor and drink water and eat stale bread, if that is the best you have.
Naturally, when a couple is getting married, they and their parents are busy, so other in-town friends and family are expected to step up and offer hospitality to people coming in to town for the wedding. As with writing bread-and-butter notes, or using black india ink to hand-write your replies, offering hospitality to out-of-town visitors to a friend’s wedding is something would-be etiquette judges have to take on in order to be without sin when they feel like casting stones at someone else’s etiquette faux pas. So, sharky does not need to provide pre-wedding and post-wedding hospitality to all of her own out-of-town wedding guests, but does need to consider offering a little hospitality to at least one out-of-town wedding guest each time she is an in-town guest at a friend’s wedding.
Normal etiquette requires that, at the end of some chore or obligatory gathering that friends partake together, that the beneficiary of their efforts offer them some kind of refreshments. A senior kinswoman is always allowed to offer to provide that hospitality on the beneficiary’s behalf, which is why the mother of the groom often offers to give a “rehearsal dinner”. It also gives her a chance to show off her good taste and social skills which are seething in frustration as she watches the bride’s mother arrange a party in which she herself has no say. As hostess, she may invite whomever she pleases, provided that a) she invites everyone who has to be present for the rehearsal, and that b) she invites both spouses or both fiances in any married or engaged couple, and that c) she doesn’t upstage the wedding itself. Often that guest list does include her own nearest and dearest out-of-towners.
In the case of “destination weddings”, or weddings where the couple and/or their families are either new in town or from out-of-town, there may be no friends to step up and make the normally-polite offers of hospitality to out-of-towners. In that case a hostess might undertake to invite them all to the rehearsal dinner as a stop-gap. She does not need to and is not expected to: adults travel on their own all the time and know how to find a restaurant and check in to a hotel and should not be treated as incompetents. It is *nice*, but it is nicer still if the whole in-town community can adopt a spirit of hospitality, and inviting out-of-town guests to the rehearsal dinner is never obligatory.