HIV, reverse transcriptase, other retro virusses.

HIV, like other Retro-virusses use reversed transcriptase (RT) to
make cDNA from their RNA strand. Every time HIV replicates 1 part in 10,000 gp-120 proteïns mutates because RT is very sloppy in copying the RNA, making it impossible to get HIV out of the body completely with antibodies (or make a vaccin).
My question is: why aren’t other retro virusses as impossible to treat as they also use RT?

Can you give an example of another retrovirus which is easy to treat? The only retroviruses I could find that affect humans are HIV, HTLV (human T-lymphotropic virus) and spumavirus (‘foamy virus’). There is no current treatment for HTLV infection besides the same reverse transcriptase inhibitor drugs used for HIV treatment. Spumavirus appears to be a possible cause of chronic fatigue syndrome, which also cannot be treated.

Perhaps the retroviruses which affect non-human mammals are easier to treat, though many of them (especially the ones affecting non-human primates) are very similar to the ones that affect humans.