It was a sensible precaution to take back in the 1980s, when HIV infection was essentially viewed as a death sentence.
Things have moved on since then, because of the massive advances in anti-retroviral drug therapy. Those self-same anti-retroviral drugs work by reducing the viral load, making HIV a manageable disease rather than a death sentence which in turn further reduces the already slight risk that an HIV healthworker represented to a patient.
In those circumstances, given the numbers of known HIV healthworkers in the UK, given the number of instances of Healthworker to Patient HIV transmission globally - 4 documented, and none in the last decade, it seems reasonable enough to relax the rules somewhat.
And the benefit of relaxing the rules might be that the fear of losing your vocation is ended, so healthworkers that suspect they might have or are at risk of HIV might be less reluctant to actually come forward for testing.