Because it might not be all that practical, natural gas is a lot harder to ship by ship than oil and the price can vary from location to location. Good idea? Maybe, but implementing it will be harder than many seem to think.
Natural gas is certainly more difficult to transport than oil, but considering the infrastructure that is currently building out to support it, it looks like LNG has a future. Doesn't hurt that Poland probably wants to have an alternative source of energy and not rely on Germany or Russia.