Memory and learning are two different things. Memorization is a small subset of learning. Memorizing declarative knowledge and personal/episodic history (cf. LLM context) are certainly needed, but an animal (or AI intern) also needs to be able to learn procedural skills which need to become baked into the weights that are generating behavior.
Fine tuning is also no substitute for incremental learning. You might think of it as addressing somewhat the same goal, but really fine tuning is about specializing a model for a particular use, and if you repeatedly fine tune a model for different specializations (e.g. what I learnt yesterday, vs what I learnt the day before) then you will run into the catastrophic forgetting problem.
I agree that incremental learning seems more like an engineering problem rather than a research one, or at least it should succumb to enough brain power and compute put into solving it, but we're now almost 10 years into the LLM revolution (attention paper in 2017) and it hasn't been solved yet - it's not easy.