I'm not an specialist, but I suspect the rationale is that you have less control of how the memory is cleaned up after use. In special, the GC can actually copy

I'm not an specialist, but I suspect the rationale is that you have less control of how the memory is cleaned up after use. In special, the GC can actually copy objects around without the programmer's knowledge, potentially making multiple copies of secrets which the programmer cannot clean up (by setting the bits randomly) later on. Without a GC, the programmer is able of knowing how many copies there are of any given secret and can dispose of them, if needed. On that note, probably writing their own "malloc" is probably a good choice. That said, I'm sure there are workarounds even in GCed languages. For instance, you can usually create C extensions which could allocate and manage memory outside of the GC's control. So, such extesion could potentially give back memory control of certain special memory regions where secrets can be stored, while everything else just goes through normal GC.