Risking being patronising... I'll have a go.
Supply and demand, wages, dealers margin, distributors margin, cost of guarantee returns and R&D expenses are the main things IMHO.
When we're talking big name companies (in high end hi fi this could mean employing as few as 15 ish people. When I was at Musical Fidelity they had I reckon about 50-80 employees and they are pretty big in this country) with international and national distributors and loads of dealers etc (glossy adds in the mags 'n all that) then if an amp costs the maker £700 in parts and labour before it leaves the factory then it will be more like £5000+ when you buy it from a dealer. About half goes to the dealer!
Point to point wiring is VERY labour intensive and obviously can only be done by hand. Not that it makes any difference to the sound.
Casework gets really expensive when we're talking 1/2" thick machined front panels etc and real hardwood end panels etc as well of course.
A lot more of it is down to you bleedin' audiophiles!!! Snob value, having to have the "component of the year", perceiving certain brands to be worth THAT kind of money just 'cos it's that particular brand, even though it may be not as good in design, build or sound as a relatively unknown brand. If myself or Firebottle announced that we've brought out an answer to Krell's (Conrad Johnson, Kondo whatever) top of the range £35,000 mono blocks and at "only" £7000 would anyone, anywhere be even the slightest bit interested? Nope. Why? 'cos it doesn't say KRELL on the front and you can't impress your audiophile mates by saying "I've just bought the new Krell GTI Super Turbo MkIII" or whatever Hence they can get away with charging that much... it's "what the market will stand"
Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)
Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco