Simple answer to that is some countries can not get the funding. The incident at Canada was down to bad organisation rather than money. But you are right about the USGP. The fact of the matter is F1 lost its American GP due to lack of interest. Now its starting to grow again due to a certain Lewis Hamilton and a great championship but even so it is dwarfed by NASCAR in the states.
Countries such as Turkey and Bahrain have governments using the race track to promote interest in their country. This is why they invest huge amounts of tax payers money.
But ironically the UK GP, the home of F1 can't even beg a penny off the government who use the excuse that the sport is rich already. True, but not the organisers. We have seen Silverstone dropped from the calendar after next year. And its not hard to see why when you see the facilities -the city of burger stands, the rivers of p*ss from overflown toilets. Now Donnington has to come to the rescue, with borrowed money. The government won't even give circuits in this country planning permission let alone any support. Yet, most of the teams are based here and we have 'motorsport Silicone valley' (central and Eastern England).
Its all about the government's relationship with the circuit.
Better relationship = more money
Crap relationship = no money or borrowed money