Offbeat Bride wrote about this in an article talking about the tradition of dowries:
"[T]he responsibility of a bride's parents to pay for a wedding. I've never been especially fond of this tradition, because I think in some circumstances all it does is foster an attitude of entitlement in those brides who would condemn their parents for choosing not to finance their extravagant tastes. That, or parents end up killing themselves (figuratively!) trying to earn the money for their child's wedding out of a sense of obligation, whether it's practical or not.
In the end, why?…
Because hundreds of years ago, women were considered chattel and the bride's family used to have to pay off the groom's family in the form of a dowry to take their daughters off their hands. After dowries went out of style, there was still the trousseau (the bride's dress and accouterments for the wedding, in addition to stuff like cake, etc.), usually hand prepared by the bride's family. Now that we have wedding vendors to make cakes and dresses for us, the trousseau has also gone out of style for the most part, and instead the bride's family just ponies up the cash....
We no longer live in the times where marriage was essentially a way to ensure that women were taken care of. Love wasn't always a factor (and still isn't, in some cultures). Teenage brides weren't uncommon, because people just didn't live as long. Girls who were practically still children themselves got married and started having children right away, because culture and religion dictated it be so. The dowry and trousseau were a necessity of those times, because they ensured that a groom would have the things he needed to support his new wife and their children to come. This is no longer the case, for the most part, as most couples who get married had acquired quite a lot of crap of their own-they don't need the "starter kits" that couples used to need."
How often does this tradition actually continue? The 2015 survey from the Knot said this:
"Tradition lives on, with parents paying for a large portion of wedding costs, but today’s couples are happy to contribute. On average, the bride’s parents contribute 44% of the overall wedding budget, the bride and groom contribute 43%, and the groom’s parents contribute 12% (others account for the remaining 1%). In 2015, 12% of couples paid for the wedding entirely by themselves, and 9% of couples don’t contribute any finances to the wedding budget.
In nearly half of all weddings, the bride pays for professional hair and makeup. Forty-four percent of brides, along with her parents, contribute to the costs for professional hair-styling, and 41% contribute to professional make-up for their bridesmaids. The average cost of professional bridal party hair and makeup services are $70 and $68 per person, respectively."
However, these statistics do only represent the type of couples and weddings that are using the Knot, which is one reason I take many of the claims of this survey with a gigantic grain of salt, such as the statement that the average wedding cost in the US is $32,641 and that the average cost of a wedding in Chicago is $61,265. That seems....unlikely to be representative of all people actually getting married. I would also like to point that every single place listed on their "Top 10 Most Affordable Places to Get Married" has a higher average budget than my wedding (I also fully intend to stay under budget because I am ultra competitive and cheap; I've already told my sister that I will beat her budget. :D She supported this completely. Fortunately, we're actually already on track to meet this goal).
I had a bit of trouble finding non-traditional wedding market statistics. I did see one statistic from a Splendid Insights market research report in an older Offbeat Empire post stating that 43% of nontraditional couples pay for their own weddings (about 20% of the wedding market identified as "offbeat" in this particular research round). Also, according to this research 48% of these nontraditional couples had wedding budgets of $10,000 or less. Offbeat Bride's own 2011 reader survey found that over 60% of their readership had budgets of $10,000 or less - 4.8% of their readership had budgets under $1,000, 13.5% had $1,000-$3,000 budgets, 18.1% had $3,000-$5,000 budgets, and 28.3% had $5,000-$10,000 budgets.