the reasons for this are 2: because the acoustics in a bathroom are better than other rooms in a house
and
you are generally more relaxed when you are showering/bathing and when you are relaxed, you sing better as your vocal tools are not restricted like they are when you are stressed/self - conscious.
because professional singers are able to relax themselves and their vocal chords without the need of a shower. that is one reason why they are professionals. if you were one yourself, or had had any singing training you would know this. lcearly you havent. please dont try and be a smart ass, you only got the last half right.
and
you are generally more relaxed when you are showering/bathing and when you are relaxed, you sing better as your vocal tools are not restricted like they are when you are stressed/self - conscious.
They´ll understand.
And why don´t they then have showers in cd-recording studios?