well...because they have no / little knowledge about cubing and therefore don't know that there are special methods to solve the cube blindfolded...they thought that we are using our speedsolving methods to solve it and how could we track the pieces going all over the cube..
like the other day...I saw a yoyo player, he was playing some weird type of yoyo...and I didn't know that yoyo also have lots of categories too..... he explained it just like rubik's cube, we have 2x2,3x3,4x4 and 5x5..for yoyo,there are A1,A2,A3,A4 and A5 yoyo types.. many things are unexpected to someone that do not know about the things..