You wrote: “Surah 2 has all the instructions about saum, no such instructions for ritual namaz.”
For argument sake, if I were to play devil’s advocate, I can poke holes in instructions about saum as well. This is how a person’s intention/goal/objective plays its part to begin with. Let me state clearly it is not the absence of any instructions of salat you are in need of, rather it is your intention/goal to nullify the Quranic salat as understood and practiced by the first addressee of the Quran.
To advance the argument, list a couple of “desired instructions” related to Salat you think God should have included in His book enabling you to perform salat.