A lot of these businesses do end up being absorbed by the big players like LVMH which grew into the most valuable company in Europe through decades of acquisitions. (The company's official name, LVMH Moët Hennessy Louis Vuitton, is itself suggestive of a merger between luxury players in unrelated markets.)
I can't think of a Swiss watch company that's operating it's own mines and metalworks, for example, or a British Saville Row tailor that also owns the herds and the looms to make the cloth it then turns into clothing. Both Hermes and Loro Piana on the other hand do this (LP is owned by LVMH).
Some small luxury brands have local, very long-term supply chain relationships that effectively offer the same benefits. As in, maybe the hypothetical Finnish maker of bespoke sailboats buys all their wood from the same sawmill (ever since 1935 when the founders of the two companies went hunting in the forest where the wood still comes from).
But of course only some materials can be sourced like this. A watchmaker and a mine are not in the same industrial league.
For example, it makes sense for Loro Piana to own Cashmere goat herds so that they can have the best possible supply of cashmere for their knitwear.
Hermes own cattle farms for the same reason, they can remove things like barbed wire from their fields which can cause damage to the finished product.
Goat and cattle herding aren't yet an industrial process like making certain grades of steel or making glass bottles (for the champagne producer) though, so while it makes sense for vertical integration in some areas, it might not in others.
The goal is basically to do things that sound impressive to justify absurd prices while employing as many people possible in as good of conditions as possible.
I wouldn't be quite so cynical about it, ultimately it's about having full control over the quality of the finished product. The material used in a Loro Piana cashmere sweater is on a different level to a fast fashion cashmere sweater, despite them both being "cashmere".