What's holding them back is provable correctness.
It's possible, nay, mandatory to constrain the outputs of the model at each step of generation in order to guarantee that a given structure or grammar is adhered to. If you can fine-tune the model with these constraints in place you can offload a lot of the effort that the LLM otherwise has to perform in comprehending correctness so it has more capacity for generating good content. To be sure, quality and quantity of data are important, but it's all too easy to introduce subtle bugs that take years to tease out if you don't adhere to the right constraints.