I was in Tonga a couple of years back and the problem was obvious then.
Trouble is these small nations (and their rulers) want all the bells and whistles of the larger countries and have nowhere near enough income to pay for the life style. Tonga has been exporting people for years - the best & the brightest go off to New Zealand or Australia, the country runs on patronage, the only "resource" is fishing licences. Who can forget the time they had TWO airlines for example - both of which went bust IIRC - when the Tongan Navy literally had no fuel available at all. They were dependent on the RNZN to carry out basic tasks such as moving supplies to the northern islands at the time
The Chinese are willing to pay for influence - I doubt it will do them a lot of good in the long-term - but unless the rest of the world is willing to stump up they're the only show in town for places like Tonga, Nauru etc etc