Why Do Aircraft Builders Still Use Rivets Instead of Welding

also, welds ever did do well will flexing of the material that was welded, even when the weld make turns two or more parts into one parts...

i have seen copper nails used as rivets...

far as i know unless it is privately owned there are no airplanes outside of military that would be made of titanium...
aluminum is used because it is cheep and bends... rivets are also aluminum (i have never seen or heard of steel being used as rivets except for the massive ones used in skyscrapers)