Why does this seem to be missing from most of the discussions about the Second Amendment

Don't forget Article I, Section 8, Clause 16 of the Constitution, which is something that need needs to be mentioned in relation to the Second Amendment. This provision gives Congress the power to arm the militia.

That was really what the Second Amendment refers to.

No conversation about the Second Amendment should neglect that this is part of the Constitution:

(Congress has the power} To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;

Most of the quotations that are taken out of context refer to this part of the Constitution and the concern that congress would fail to arm the militia in preference for the federal army.

It's really annoying me that the Second Amendment is not only misquoted and taken out f historical context, but it is taken out of Constitutional Context:

The Constitution, as originally adopted, granted to the Congress power --

To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions; To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress.

With obvious purpose to assure the continuation and render possible the effectiveness of such forces, the declaration and guarantee of the Second Amendment were made. It must be interpreted and applied with that end in view. US v. Miller, 307 U.S. 174 (1939)

I'm sick of people pretending that the first part of the Second Amendment is irrelevant to the Second.

And even sicker of people who would make any part of it irrelevant.

The right of the people to keep and bear arms is tied to the well regulated militia which is necessary for the security of the free state.

It must be read as a whole, not a part.