Is there a reason that we don’t just make the flag out of fire resistant materials?
That is entirely up to the manufacturer.
Because the proper, approved, method for disposing of an American Flag which has become unserviceable (unsuitable for display) due to damage, wear, etc. is to burn it, in a proper ceremony with respect.
Not like this sh!thead in the story did, of course.
Google it, or check the American Legion site, or any of a number of sites dedicated to proper care and display of Old Glory.
US Flag Code, TITLE 4 > CHAPTER 1 > Sec. 8(k) states:"The flag, when it is in such condition that it is no longer a fitting emblem for display, should be destroyed in a dignified way, preferably by burning"