Growing up reading LOTR, Silmarillion, etc and ignoring the portrayal of Balrogs in LOTR movies, In the actual text I see: "and its wings were spread from wall

Growing up reading LOTR, Silmarillion, etc and ignoring the portrayal of Balrogs in LOTR movies, In the actual text I see: "and its wings were spread from wall to wall" (referring to the Balrog confronting Gandalf). Wings in the sense that gliders have wings, they can float/glide down but don't expect them to fly into the sky. If they could fly why didn't the Balrog that fought with Gandalf in Moria at Khazad Dum fly upwards when Gandalf broke the bridge? They ended up both falling, tumbling down to the abyss.