"Why are you waiting?"

Translation: Warum wartest du?

[J.P.MAP]

Why not 'Warum Sind Sie warten?' as well...

[az_p]

Warum warten Sie? would be possible, but German does not have a sentence construction like what you wrote.

[biertopf]

Yep - I guess you tried to form a present continuous, but there are no continuous tenses in German.

[J.P.MAP]

thanks