How sure are you about that? I've never looked closer at how a large LLM with mixture of experts architecture switches between expert modules, but staying on roughly the same topic for the use (as it often would when editing the same codebase), I wouldn't be surprised to see the switches of composition are fairly rare, fairly small, and to the extent it happens it's repeated reads from the flash disk rather than writes it tends to cause.
If one is to use these on hardware that can't keep everything loaded I guess someone should examine how it works out in practice. Interpretability may be be a too much to ask, but I can't spontaneously see any reason why the experts can't at least be pushed to incorporate what's needed to remain the good choice for a longer segment.