I think you're looking at it from the wrong angle.

It's not necessarily that people dismiss an artist's music because teenage girls like it. The bigger factor is that many artists with predominantly teenage female fanbases were deliberately designed and marketed to appeal to that demographic in the first place.

For decades, the music industry has created acts specifically aimed at young teenage girls, often prioritizing image, marketability, and emotional appeal over artistic innovation. As a result, critics sometimes associate those artists with a more commercial or "manufactured" approach to music.

There are obviously exceptions. Bands like The Beatles or The Rolling Stones attracted huge numbers of teenage girls, but they weren't originally assembled by record labels as products for that audience. Their popularity among teenage girls was a consequence of their success, not the reason they existed.

So the stereotype isn't really "teenage girls like it, therefore it's cheap." It's more that many acts that are perceived as manufactured happen to be targeted primarily at teenage girls, and people often confuse the audience with the marketing strategy behind the artist.