When I enquired why not, was told 'staffing issues'. Humm.
When i was an approach controller in Oz, it was explained to me that the RLSALTS were only surveyed in relation to the CTA steps. Sometimes the RLSALTS were lower than the CTA steps in some locations, but that nothing could be guaranteed after the initial surveying, ie when new towers were constructed, new high rise buildings, funnels on factories, phone polls, tree tops, etc. So if the steps were changed then it would be 're-surveyed' and accurate again... But still unlikely to be used in G...
But it does lead to the question, how often are they surveyed now? Even if the airspace doesn't change? I suspect the risks are quite low... still...
There was an awful hullabaloo about the gas power station near the Westgate a few years back. (not about height per-see but about minimum height to overfly it, which effectively makes it a (R) LSALT); I believe the funnels on that one lost some 100 feet from original design...
There are also issues with an aircraft been given a RLSALT for a particular area in G then making a tracking adjustment where a new RLSALT may be needed but never followed up on by PIC or ATC. Some "terrain boxes" were quite narrow; it's just a liability issue.