1) It keeps the male ever vulnerable and open to Mistress' swats of correction upon bare bottom, nipples, or genitals.
2) It permits Mistress to examine the progress of any exercise or dieting regimen She may have directed for Her boy.
3) It keeps the boy humble and more compliant (hard to be argumentative when kneeling naked before a fully clothed Woman)
4) The male is ever ready for use by Mistress' strap-on, nipple clamps, Humbler, ball weights, or anything else She wishes to attach to him or use upon his body.
5) When friends are visiting it allows them to easily see who is in charge.
6) Males are hard on clothes and so keeping him naked helps them to last longer.
7) Her other pets don't wear clothes, so why is he any different? (of course they all wear a collar and tag)
8) It reminds the male that Mistress makes all the decisions, including what he can and cannot wear.
9) If he is locked in a chastity device it keeps it in constant view, underscoring his totally submissive status.
10) Because She said so, that's why!!