Money is important for what it can buy.

Some people want money so that they can feel secure in the future. That is they want to make sure that they Will always have enough of the commodity.

Others want money asa matter of prestige. They can show off their accomplishments and think that they are better than others if they have more money.

Money has been made important for the above reasons and perhaps others as well.

nations want money for the same reasons as above plus they want and need money to provide for the nation for such things as roads, bridges, public buildings and defense.

Men having more money is the equivalent of the male animal being stronger. Just like in animal kingdom, the female mates judges the suitability of male on their physical strength which translates to better ability to protect her and her children during danger and providing for her, female humans tend to choose mate generally according to wealthiness of the male for the same reason, better ability to provide for her and her children because money can buy resources (food, clothing and shelter) and better protection -> money can buy security alarm system and bodyguards and etc. The extreme form of it of course is gold-digging which is a frowned upon practice but generally, all else equal, a relatively wealthier man would always be more attractive to a female than a less wealthier.

Nations are just a collection or aggregate of men, if all men are trying to make more money to survive, then naturally this becomes the priority of the whole nation.