It allows/invites a challenge from a weaker leader who suggests selling some gas to get some money. If there is no option and no flexibility there is no alternative, no challenger.
And that goes for every player. Want to be Germany and not have someone outflank you and say 'lets take the cheap gas from russia' - take the gas off the table. Want to be India and still get half off your energy? Want to be the US and get to sell a ton of gas to europe?