Price, durability, prestige, feeling, performance, quality control, etc. etc.
Often times, people equate high prices with quality. So Butterfly being more expensive must be better.
But on a more serious note, some people are used to playing with Tenergy and its Spring Sponge technology. Yes ESN (European rubber) has tensor but some players will swear tensor does not feel the same as spring sponge.
If you look at top players, overwhelming majority use Butterfly. My club coach pretty much uses that as an excuse and sell Butterfly equipment only. There is something to be said about that argument. After all, top players want every little edge they can get so if that means Butterfly, then they will stick with Butterfly.
On the other hand, Lebrun brothers switched from Butterfly (D09c I believe) to Tibhar (K3 now) and they have not missed a beat. Kao Cheng-Jui switched from Butterfly to Andro and he seemed to struggle a bit in the beginning but is doing very well now. Oh Junsung switched from Butterfly to Tibhar but seems to be struggling with adapting to European rubbers.
This is a bit of cause-and-effect. Butterfly sponsors a LOT. They spend so much time, effort and money on sponsorships that "getting sponsored" in many countries is, or has been, analogue for "using Butterfly".
It's easy to then think that Butterfly equals good, because good players use Butterfly.
So it is a matter of preference and where you can source your equipment (it is impossible to get any discount on any Butterfly equipment; Butterfly is very strict with its distributer policy and will revoke your ability to sell Butterfly products at any time.
This is just perfect marketing. They're making the brand "exclusive" which means that companies that want to look exclusive too, need to barter for distributorship. In Western Europe at least, there's only one official distributor per country. So if companies have to be good to be able to sell these products, the products have to be awesome, right?
Butterfly complements this with more marketing factors:
- their own rubber hardness scale
- a very comprehensible rubber catalog
But what they also do is generally release good products, with a high level of consistency in QC (rubbers) and good standard of finishing (blades).
ESN brands have released what, 5-10 hybrids with different hardnesses and ideas per brand? Butterfly just did 2 (Dignics and Glayzer 09c) with a pretty clear picture of the target audience for each. I honestly get completely lost in ESN brand catalogs. And that's besides the obvious marketing issues with horrible websites and little to no (f)actual information for brands like Tibhar and Donic.
Andro is making a good point about providing specifications, including sound clips of their blades. I personally think though that their product lines lack courage (pizazz) and international targeting. Most of it is rather bland and/or too German-focused. Even if Germany is a huge market in Europe, I think it's a problem.