We were doing zero and few-shot classification with LLMs since before they could reliably complete whole sentences. It’s an easier task than generating coherent text. The model needed to be tuned for classification (not generation) and for the domain, but it would often succeed at new classification tasks with a simple description.
I guess given the huge advances in LLM since then, these models probably achieve much better accuracy on a wide range of domains with lower effort compared to what we were doing, which makes it compelling as a product. And yeah, the models probably were already good enough a few years ago too. Other factors include how easy it is to release products at high speed now, and the desire in the industry to reduce token spend.
Zero-shot encoders even pre-date LLMs. People who worked in NLP in the transformers "BERT-era" may be familiar with natural language inference (NLI).
Decision models are really not much different than that, but (usually) scaled up to bigger causal models.
If you are looking to do Jev-like things with smaller models, check into NLI.