It probably still does not activate 100% of the virus. Some still remains and reactivates later.
> "This molecule has great potential to advance into translational and clinical studies."
> However, the drug has still not been tested in people who are HIV-positive.
To be sure that this new treatment is useful you must try it in a double blind experiment with many patients for many years.
Now, it's only an interesting idea with some in vitro support, but it's no a real cure. The title "HIV flushed out by cancer drug" is an optimistic exaggeration.
Having said this if I was infected with HIV this is exactly what I would be doing (ie treating with drugs that suppressed viral replication while chasing the latent virus out of hiding).