They weren't being imperial for their people.
It was so they could brag to other royals and rulers that their kingdom was bigger.
The people were resources and toys for the rulers' entertainment.
>Great powers are forced to manage the international system, or become a client of a great power. There are benefits to being a great power.
>When 1 great power builds weapons, everyone else is forced to too. This is called the Arms Race.
>Colonialism is one example of the Arms Race. If you didn't join the party, you were going to lose.
>Great powers put international politics above domestic politics. Its why we see the US do things like spend heavily on the military and get involved in unpopular wars.
The British empire was an aftereffect of a long power struggle of several European countries, which was, for its participants, way more existential than you admit it to be. Look at the Seven Year War, the first truly global war in history. France, England, Prussia, Russia, Austria etc. stood to lose a lot if they lost decisively, and were strongly incentivized to improve their militaries and navies to prevent precisely that.
The same scenario was replayed during the Napoleonic wars. One power eventually emerged victorious, it now had the best navy in the world and no peer competitor left. (It was also gripped by dangerous internal struggles, google "Peterloo".) That is a situation with a single person having a lot of hammers and the rest of the world looking like a nail park.
Obviously I'm making a vastly reductionist statement, but I don't think I'm wrong.
End of the day, an ego's purpose is to brag. Otherwise what is the point of having an ego? That's why wise people try to shed their ego lol