I'll take a bite at this.
Marketing
Marketing from their actual professional racing kits get people onboard to view them as a “premioum” brand even though most of their street geared kits might not actually have much in common.
Reputation
I personally think because the major brand names have good reputations that they have built over the years, people get wow'd by the brand name and not look more deeply into the features offered by each kit today.
I can't justify the price difference btw ST and KW V1, but their reputation are thesame becasue they are both made by KW. The KW V3 to me is the only true KW prestige kit.
Warranty
Warranty support is pretty identical as almost all the companies require the kits to be removed from the car and shipped back for inspection before a warranty replacement is sent which could take months.
The lifetime warranty is also not worth it as wear and tear is not covered, and after 5 yrs most owners will probably have sold the car or close to being sold. Shocks will probably need a rebuild after 5 years and it won’t be covered under warranty, so I do not personally get why the KW V1 costs much more than the ST.
I usually prefer warranty that allows me to deal with my seller or installer rather than directly with the brand.
Corrosion protection
Most of the brands above advertise their kits as stainless steel when they are not 100% stainless.
Comparing $700 ST suspension to $1100 KW V1, the galvanized steel vs stainless Steel fronts does not justify the extra $400.
The height only adjustable brand name coilovers are a huge disappointment for what they offer and are not even on my radar these days.
Koni is chrome plated
KW V1 & V2 are INOX Stainless Steel fronts, rears are powder coated.
KW V3 is full INOX Stainless Steel
ST is galvanized steel, rears are powder coated.
H&R (Premium and Ultra-low) is Stainless Steel fronts only, rears are powdercoated.
FK is Stainless Steel fronts only, rears are powdercoated.(at least I think so for most of the coils they have. Not sure about the Silverline X)
B&G is powder coated
K-sport is Teflon coated
V-maxx ??
Bilstein ??
Higher grade metals on perch & shocks
There are two categories here, cheep and quality. Raceland and cheaper eBay coilovers seem to be sub-par as owners have complained.. V-maxx used to be cheap but they have stepped up their act and in my books are classified alongside the other “premium” brands here.
Features
This is how I personally shop. Best bang of features for my money.
All in adjustability, top mounts, end-links etc.