Bids and asks are making bold predictions about the current value of an asset. If they are wrong then anyone can enter the market and make a profit. Bid/ask of 99.90/100.10 means that the true value of the asset is between 99.90 and 100.10, because if it was really worth $100.20 someone would come in and buy up all the offers through $100.19 (give or take a bit for risk management, fees, and minimum profit targets). Usually what happens though in these markets is that the bid/ask is $95/$105 and true value is something like $101 but no buyer wants to pay a $4 spread and no seller wants to pay a $6 spread, so no trades happen. The last price could be $90 from back when the asset was $90/$100 true value around $95 and someone really needed to get out and was willing to pay (or didn’t know).