We are currently in the Modern Age and as Time changes everything the Singers we all knew also changed with time. So Singers as we knew them when we were young are vastly different from how Singers look now. Part of the reason is mainly that when I was young MUsuicans or Singers only had to Sing and there was no Music Video where they were going to showcase the Artist but now that the Times have changed the LOOK of Artists and Singers are pretty crucial as that also adds an added element to the Music itself. There are definitely a lot of reasons for this change in Looks but let me articulate a few of them here.
The Marketing Aspect of the artists and their Records have changed drastically wherein Record Labels do intend to market the Songs and their Singers as Sex Symbols where the artists are styled accordingly with flashy outfits and Make Up. By doing this, they create a Buzz around the Music as in the Modern Age Songs and Lyrics are not the only thing that matters. YOU NEED TO LOOK GOOD AS WELL.
There are also Artists that are genuinely Charismatic and have a pull of their own and in this case, I will say that the Artist deserves their Attention as he/she is not doing anything fake to attract attention. They are just SEXY on their own.
Finally, we have Social Media where Singers are using various Platforms to promote their Music and Music videos it definitely helps to have a Sexy Outlook when your Fans are visiting your Profile so that they get hooked to the Artist as well rather than just the Music.
I will also say that there are indeed Artists and Singers in this Modern Age who doesn't give a sht about being Sexy and make just Songs and are still very very successful but those are definitely only a few of them.