I wouldn't say there has been extensive discussion, but some people have discussed it.
In the case of Surah Ikhlas, the reason it was revealed (Sabab an-Nuzul) is itself a reasoning for the existence of the "Say" in its beginning.
There are many reported narrations for why it was revealed but what they have in common is that it was revealed at a question or demand by the Kuffar to the Prophet (SAW) to describe Allah.
Hence, it is almost like Allah saying, "As a response, say this, this, and this."
Although most tafasir do not mention this explicitly, they imply it with the mention of the Sabab an-Nuzul. Ibn 'Ashoor, however, mentions it explicitly in his tafsir.
Other reasons are also mentioned in some tafasir for the "Say."
It should be noted that most of the verses starting with "Say" have obvious reasoning for it. That is probably why most scholars didn't discuss what was obvious. For example:
Say, [O Muhammad], "If the home of the Hereafter with Allah is for you alone and not the [other] people, then wish for death, if you should be truthful." (2:94)
The context is a back and forth debate with the Jews, and Allah is teaching us what to say in this debate. I would say a large majority of the "Say" verses are in a similar context of debate with Jews, Christians, or Mushrikeen.
Only in the contexts where it is strange would discussion be required.
That said, in the tafsir Mafaateeh Al-Ghaib, 43 benefits are mentioned for the "Say" in the beginning of Surah Kafiroon, and three are mentioned for the "Say" in Surah Falaq.
