How many cubic meters of gas have been wasted since 1971?
The flow of gas doesn't stop just because you put the fire out. So now instead of combustion products being released into the atmosphere, you have natural gas. This is not an improvement. In fact, that's why they set the fire in the first place, because having unburned gas floating around is a big problem.
In theory you could put out the fire and capture the gas, but that's a fairly tall order. You'd have to install the capture equipment without either being burned by the fires, poisoned by the gas, or setting off an explosion when the gas concentration hits the right amount. Then you have the pleasure of trying to sell the captured gas at low wholesale prices on the international market.