John 5:4 ...Where are you?

As I was doing Bible study yesterday, I misread a reference that said John 5:24, and I read it as John 5:4. Well, I turned to John 5:4 and it was not there. 5:3...5:5... I thought there was a misprint in my Bible. I went to another Bible and looked...it wasn't in that one either. Ok, then I thought it was the translation. I was reading from the NIV. I found a NAS translation. The verse was there...I was thoroughly confused. As I looked at the NIV again, there was a note and the missing text was in the note. As it turns out, a portion of 5:3 along with 5:4 has been omitted from earlier manuscripts. It is very interesting to read. Here is the text from the NIV found on Bible Gateway along with the footnote:

John 5:3-5 (New International Version)

3Here a great number of disabled people used to lie—the blind, the lame, the paralyzed.^[a] 5One who was there had been an invalid for thirty-eight years.

Footnotes:

1. John 5:3 Some less important manuscripts paralyzed—and they waited for the moving of the waters. 4 From time to time an angel of the Lord would come down and stir up the waters. The first one into the pool after each such disturbance would be cured of whatever disease he had.

Verse 4 gives us further explanation of verse 7:

7"Sir," the invalid replied, "I have no one to help me into the pool when the water is stirred. While I am trying to get in, someone else goes down ahead of me."

The NAS includes the text for the remainder of verse 3 and verse 4 with a note explaining that earlier manuscripts leave it out.

I thought it was neat that I stumbled on this only because I misread a reference. I am curious as to why it would be left out.