Money is one compelling form of power, sure. And one a regular citizen also sort of understands, albeit not at scale.
But being able to takeover ports, build bases, make claims on other nations is a way to extend sovereignty far outside your borders, that is power that sometimes yes will be used to make money. But sometimes there are indeed other more direct interests that need serving, that these debts will lever them access to.
Overall I think it's more harmful than useful to flatten the interests down to being all about money. States have other things they must also do & maintain, and not all of them are easily buyable.
They give loans backed by resource rights to build up some infrastructure, roads and ports particularly, then wait for them to default. Now they have resource extraction rights as well as the infrastructure needed to extract those resources. Cash is less important than power, China means to reshape the international order because they're tired of being a second class player in global affairs.
Money can't buy everything. But if you lend the money and the borrower can't pay it back, suddenly you can ask something that normally can't be bought directly with money.