Equipment cost and electric cost have ZERO effect on market cap, and have no direct input into price at all.
Price effects the profitability of mining, NOT the other way around.
The same number of coins are generated no matter how many - or how few - miners are competing for the block rewards and block fees - and number of coins generated is what affects price, NOT how difficult it is to mine those coins.
Market cap is STRICTLY the product of the number of coins in existence times the price per coin.
https://coinmarketcap.com/1 Bitcoin Bitcoin $40,521,038,263 $2468.65 16,414,250 BTC
@op market cap by definition is coins x price so 2468 usd x 16,414,250 coins = 40,521,038,263
your question is the same as asking why does 2 x 4 = 8 the answer is by definition it does.
basically the human race agrees to it! amazing we humans can actually agree to some things.
as to the cost of the gear to mine btc
Hash rate is 5,094,526,985 gh is about
410,000 s-9s so say 1132 + 108 psu + 130 shipping = 1370 usd
so
410,000
1,370
561,700,000 say 600 million in gear