LLMs seem to care about getting things right and improve much faster than engineers. They've gone from non-verbal to reasonable coders in ~5 years, it takes humans a good 15 to do the same.
The people training the LLMs redid the training and fine tuned the networks and put out new LLMs. Even if marketing misleadingly uses human related terms to make you believe they evolve.
A LLM from 5 years ago will be as bad as 5 years ago.
Conceivably a LLM that can retrain itself on the input that you give it locally could indeed improve somewhat, but even if you could afford the hardware, do you see anyone giving you that option?
LMM "memory" is a larger context with unchanged neural paths.