ok some math
if OP uses a 15k cost and a 10k sell
well imagine there were 25 people making half a bitcoin ($7.5k cost $5k sell)
12.5btc is worth $125k
now we have 25 people sharing 12.5btc so for $7.5k cost they are getting 0.5btc ($5k)
now if 1 person drops out due to a $2.5k loss
now it has 24 people sharing 12.5btc so for $7.5k cost they are getting 0.52btc($5.2k)
now if 1 person drops out due to a $2.3k loss
now it has 23 people sharing 12.5btc so for $7.5k cost they are getting 0.5434btc($5.434k)
now if 1 person drops out due to a $2.056k loss
now it has 22 people sharing 12.5btc so for $7.5k cost they are getting 0.5682btc($5.682k)
.. and so on until profit for 16 remaining people
What if this your assumption doesn't hold. For instance, what'll happen if no miner want to leave the business at a decreasing revenue of their reward?
Miners wants or desire has little to do with it.
When the electricity company turns off the power for non-payment, or the loans on the asics are not paid and the asics seized as collateral or the owner of the ware house locks the miner out for non-payment. Then the miner is done.
Franky1 biggest misunderstanding is that he thinks someone will always be able to earn a profit in PoW,
the problem with that thought process, is government confiscations and resell of bitcoins,
will always be cheaper than the current production costs, which insures that PoW is a dying tech by an economic blade.
25 people mine bitcoin , all 25 are losing money, how does bitcoin survive using PoW, easy it won't.