They probably calculated that keeping their contractual obligations to the west who are the main supporters outweighs the monetary benefits Russia gets from the sale of the gas.

Obviously it’s because the gas goes to Europe, which until recently was very dependent on Russian natural gas. Europe is Ukraine’s ally. Ukraine needs Europe’s military aid and shutting off the gas would make things hard for Europe and potentially upset them.

I'm guessing fucking over the population of your main supporters in the war isn't the best strategic move. But if the contract expires they have a solid excuse, also Europe has pretty much figured out it's gas issues at this point

Fair warning to those importing it.