> to believe creating some vague random re-brand is actually better for them, it makes
> no sense to me, but they seem to all believe it.
It's a marketing thing. Once customers come to recognize and respect a brand, they're more likely to purchase it, since most buyers don't do useful things like research before making purchasing decisions. So, having a brand that other vendors share dilutes their own brand identity. If EB says that their WPB fabric is eVent, then in the eyes of the average consumer, the EB (or First Ascent, or whichever) brand is weaker, because the eVent brand appears on stuff from all sorts of other vendors, including REI and The North Face (etc), and then it's harder for EB to convince the least common denominator consumer that their WPB is better than the one that REI and The North Face use.