In democracy, citizen decide how the tax money is spent by voting, usually it’s an indirect vote : you elect people to vote the budget, which makes sense considering the difficulty on the tax. But typically, left wing will put more money in education, healthcare, and rehabilitation programs while right wing will put money in police, militaires and supp rt outsourcing essential services to private corporations. Stuff can be complex as you need to pay pensions, state worker, fulfill international commitment (EU budget, NATO budget) and maintain all the existing infrastructures, and only then you can invest/re-allocate budget (which can trigger an outrage, cutting welfare expense or closing a hospital can have dramatic consequences for citizen)

If there isn’t enough money se government can borrow money, typically they don’t go the bank but say they need X billions for Y years and find investor ready to lend them this money (it tends to be quite safe, do you foresee US or Germany not paying their debt in 5 or 10 years?) alternative is to print money (aka inflation) or raise taxes. For structural investment that will bring monee, it makes sense to pay them over 10 years with the extra tax yield thanks to the new highway/university/dam. However, it also means that instead of “taxing the rich” you borr w their money and give them back, while us commoner do n’t directly see our tax money ney back