Mining rigs are not profitable.
Calculate that if you bought 1 btc when btc = 4000$ then you get %70 in few months.
But if you bought a mining rig or asic? then you will still trying to get roi.
thats all simple
Yes, but nobody can guarantee what will happen to bitcoin or any other altcoin the next day. It can be much more profitable than investing in mining risks, but the latter on the contrast is almost risk-free.