Cairns rental bond dilemma

Yes, also confirmed by census data, some time ago Townsville surged past Cairns in rental bonds held by RTA. Now I have always thought this should be pretty good data given it is backed by statutory compliance. I don’t know what effect defence housing has on Townsville. Have the number of rental bonds lodged in Cairns really not risen in the last five years?
How exceptional this is becomes clear after the task of sorting the regional data for large council areas in Queensland. This is over the five years to December 31:

What this seems to imply is that the decline in rental vacancy rates we have seen in recent years in Cairns is not because of more renters but restricted supply? I will come back to this in context of rental vacancy data from SQM and HTW and relatively high rents in Cairns.
Some of the Brisbane numbers are extraordinary relative to population growth and caused me to check some details. Postcodes 4101 and 4102 around Southbank and Woolloongabba rental bond growth above 25% over the last year.
Build it and they will come?
*Note: Sun Coast includes Noosa, and Rocky includes Livingstone.