Look at who the tools are marketed towards. Writing software involves a lot of tedium, eye strain, and frustration, even for experts who have put in a lot of hours practicing, so LLMs are marketed to help developers make their jobs easier.

This is not the case for art or music generators: they are marketed towards (and created by) laypeople with who want generic content and don't care about human artists. These systems are a significant burden on productivity (and fatal burden on creativity) if you are an honest illustrator or musician.

Another perspective: a lot of the most useful LLM codegen is not asking the LLM to solve a tricky problem, but rather to translate and refine a somewhat loose English-language solution into a more precise JavaScript solution (or whatever), including a large bag of memorized tricks around sorting, regexes, etc. It is more "science than art," and for a sufficiently precise English prompt there is even a plausible set of optimal solutions. The LLM does not have to "understand" the prompt or rely on plagiarism to give a good answer. (Although GPT-3.5 was a horrific F# plagiarist... I don't like LLM codegen but it is far more defensible than music generation)

This is not the case with art or music generators: it makes no sense to describe them as "English to song" translators, and the only "optimal" solutions are the plagiarized / interpolated stuff the human raters most preferred. They clearly don't understand what they are drawing, nor do they understand what melodies are. Their output is either depressing content slop or suspiciously familiar. And their creators have filled the tech community with insultingly stupid propaganda like "they learn art just like human artists do." No wonder artists are mad!