Nox. "Why do people sing when they're awful?". Thst may be the most important question asked in the last five thousand years!. I don't profess to know but I suppose it is because of human nature itself; we don't always hear ourselves as others do. That goes for things not musical as well.
I am of an age that attached importance to a singer using good diction first of all even in pop music. I am forced, by my wife, to watch 'American Idol" and you cannot imagine how painful that experience can be to one like me. I'm not a snob but I grew up listening to pop singers like Ella Fitzgerald or Frank Sinatra even up to some latter day singers, Striesand for one. They had excellent diction, stuck to the line of the music, never strained their voices. My preference in singing is serious music; opera, choral, but these singers I mentoned were just as good at their craft as those stars of the operatic world.
'American Idol" makes me tire after about five seconds; everyone sounds pretty much alike, I can't understand a word they say{sing), the most important thing seems to be a vocal style that wanders all over the place...in a word "awful" I understand that my view is not shared by all. On the whole I think pop music is made up mostly of fluff, which fluff is not noted for standing the test of time. That is the best way I know of how to define good music, how long is it likely to be around?
So, to reply to your question, who knows. I am reminded of an old line about the description of a gentleman. ? "A man who can play the accordion but who chooses not to"
An awful singer is one who can't sing and who chooses to do so.