Why won't she wear her "Cute" pajamas?

My girl has a pair of pajamas with a trap door in the back. it doesn't attach anymore and it exposes her a little but she looks adorable in them. I always tell her to put them on at night but she rarely will and she really never gives a good reason why she wears her boring PJ's instead of the ones she looks so cute in. I don't get it, What could possibly be the reason?