It is important for some people. How can you decide what others need or don't?
About the money, I guess it doesn't have to cost a fortune if one investigates properly. I agree with you on the inviting people thing though.
I want to get married if I meet the right person and sure as hell very few people will be invited.
Yeah, the size thing I find is usually more a matter of family pressure than of the couple's desires. Obviously there are plenty of couples who say "this day is about us, so if we don't want a big wedding, we're not having a big wedding." But I see many times where the couple wants a small wedding but the parents want to invite everyone who has ever been in their child's life (and/or they are super worried about "offending" someone by not inviting them), and the couple loses that argument. And when someone's parents are paying for the wedding (which happens a lot), they kind of get a certain degree of sway there.
On principle, I agree that the oversized weddings are silly. And I do think that the couple should really be the deciding people. But I recognize that relationships and parental approval tend to be very important to a lot of people and that for them, the benefit of keeping everyone else happy ends up being considered worth the hassle of the big wedding. (And hey, upshot: a lot more wedding presents)