I'm sure other places, cities etc have significant trees on registers and they get bi-annual or annual check ups.
The issue seems to be that the trigger for arborist action is often a negative one, when things are going bad, the tree failing, losing branches etc.
Whilst it may be hard to check every tree every year you'd certainly expect that significant trees be checked. What if the significant trees reside on private properties? ... does happen. I know that locally I have attended to properties to quote the removal of a tree. I usually try to check on the internet but many times end up calling the council to discover a Significant Landscape Tree Protection Order (SLT VPO). These are singled out trees, that protection order is not a blanket one for the city.
The owners sometimes look surprised and sometimes disgruntled for various reasons.
The issue is that those trees aren't cared for or reported upon, and sometimes people dont even know they have them!
If there was a pro-active approach where these trees were inspected, the longivity and safety would increase. However at the moment they get nothing, some of the trees will also get mistreated so they die in the hope the approval for removal then goes through.
I think an easily accessible website for all Significant trees would be a start, a site that provides details and when last inspected and what was on that inspection. Of course that will bring all sorts of issues out however if looking after significant trees is the goal then you need a plan.
A pro-active approach is what cities need to implement. It's caring for healthy trees that matters to, parking your tinnie there and chaining it up to the trunk whilst the bungs have been pulled and you wash it out isn't the best thing for a tree.