It's cheap for the whales but not for all of people. You must not think if all of people are having a lot of money and they can buy anything especially bitcoin. 7k dollars for each bitcoin is too much for the small traders like me and maybe some people too.
In my estimation $7000 is the lowest point of bitcoin prices this year, so, it is indeed very profitable to buy at current prices, I don't think we should buy One BTC for investment and if we have enough money to buy half a BTC, why not ? But in a market condition like this, honestly I would rather buy some altcoin for my investment assets rather than buy BTC.