Can someone explain me why the hashrate going up is good for the price?
I mean, I know economics. I know that the supply is a function of price and cost. So if cost goes up for miners, then the supply will shrink. But why the hashrate should be consider as proxy of cost?
It's is quite possible that the cost for most of the miners is actually going down while the hashrate and difficulty are increasing. If there is a consolidation of the mining market, big mining farms are making economy of scales, so their margins increase while the hashrate increase too, so they could very well selling a greater proportion of their mined coins to enjoy their high margin.
All of that to say that I am not convince that the hashrate is a good proxy for evaluating the cost of mining BTC, therefore not necessary a good indicator for the future price of BTC.
I agree with you. There have been lengthy arguments about "hashrate follows price" or "price follows hashrate" for years now. I'm in the former camp.
Also: supply is not a function of price and cost in the case of bitcoin mining. Supply is pretty much constant, miners just fight among each others over the fixed-sized cake. So only way in which mining influences price is by one variable: the percentage of coins sold by miners into the market.
I think this percentage is increasing with falling price, up to some point... some miners will reach > 100% and switch off. If they want BTC they'll buy instead. Mining efficiency (of the remaining miners) increases and cost decreases. Their selling-percentage decreases. All this has positive effect on price, further decreasing the percentage that has to be sold to cover cost. I'm not sure we've reached low enough price (or competitive enough mining landscape) for this to play out to a meaningful extent.