In public finance, there are multiple approaches to determining how to use the public budget. There will always be the standard expenditures that will have to be costed in, the overheads to cover the public service.
Then there are past liabilities that will need to be paid for. But then, each time, the government can make a decision whether those liabilities are still worth their while to continue financing.
After which, we determine the infrastructure and other investments essential for development of the society. When it comes to investing into infrastructure, the government will definitely need to meet needs, but they might have to ask themselves what kind of social benefits are generated in order to work out whether the price tag for fulfilling those needs make sense.
This is the realm of externalities. And the reason we care about that is because the free market would not. If private benefits exceed private costs, then the free market will find its own means of fulfilling those needs. When there are externalities, the government has to step in. From a business point of view, where there are negative externalities, it is a revenue-opportunity for the government. And where there are positive externalities, the ruling political party can get some political mileage out of it.
Such is the interaction across politics and economics that is worth a bit more attention.