WHY DO THEY DO THIS

speedrunning isnt about getting the best gead
its about beating the game as fast as possible
other examples of popular ways to play that include this are in pvp style games
sharpness V iron sword > diamond sword and such that leads to cheaper and faster ways to get the same result

netherite generally takes longer to get while speedrunners want to have the best time not gear. also most speedrunnersget iron tolls beacuse diamonds are also harder to get