This is one of the conflicting attitudes that society places upon various groups. The one we're talking about here simply happens to be aimed directly at children, and all younger adolescents legally designated as such (the public is conditioned to see little to no difference in the two because of this synthetic technicality).

From a cultural standpoint, adult beneficiaries of a synthetically prolonged and rigidly defined paradigm of "childhood" want those under the legal designation to remain children, and thus remain forcefully dependent; under their control; out of the major aspects of the labor force; and a captive audience to indoctrination methods posing as "education," etc., for as long as possible.

But on the other hand, the marketing aspects of the economic system manufactures products that feed into the desires of younger people to fit into the adult world, because unlike the sub-cultural world they're forced to be part of 24/7, the adult world offers them (for the most part) freedom of expression and choice. These outfits allow them to sort of "cosplay" as an adult for a single night, when transgressive boundaries normally heavily enforced are supposed to be permeable for the sake of fun. Doing this outside of Halloween is much more difficult, and has to be done largely outside the direct observation of adults with the most control over them (e.g., parents, teachers, sometimes older siblings, coaches, or other "authorized" adult overseers). Now, of course, the pundits of cultural correctness strive to take even the perceived freedom of this single night of the year away from them too.

After all, the market is, in its own way, transgressive to culture if it's believed that following the status quo to the letter is inhibiting many potentially profitable ventures. These Halloween costumes allowing underagers to "cosplay" adult roles even as they cosplay super-heroes, pirates, Star Wars characters, princesses, etc., is one of these. Every company does have to worry, and pay much lip service, to maintaining a "good" (i.e., culturally approved and socially acceptable) image, of course, but that doesn't prevent them from attempting to push boundaries if that is where the money is. CP, btw, was never highly lucrative when it was legal in some parts of Europe and Japan during the 1970s and elsewhen, which is why most corporations find it more advantageous to pander to public sentiment when it comes to this... except for the most subtle of transgressions, including secretly making the Olsen twins videos be as appealing to adult admirers as it was to their plethora of child fans. Transgression against powerfully entrenched boundaries always has to be done with care, never with absolute impunity, and those who run the corporations know this.

As for government agencies, they want children to adhere to the common paradigm or mirror adults entirely based upon whatever happens to be convenient for the legal system in any given instance. When it comes to freedom of choice... they're usually forced to stay in a "child's place." But if they happen to commit a certain crime, they can be declared "competent as an adult" if it's expedient to put them away via an adult trial.

This ironic state of affairs is similar to the types of conflicting images directed at women in regards to sexuality. On the one hand, contemporary women are often told in official circles that it's perfectly healthy and normal for them to enjoy a sex life, to have sexual desires, to derive pleasure from recreational sexual activity, and to use sexual expression as a way of facilitating greater independence. But on the other hand, they're constantly bombarded with "slut-shaming" sentiments that seek to deride their character and inherent value if they do not try to rigidly adhere to either a near-celibate lifestyle when single, or to maintain nothing more than a strongly monoamorous relationship that lasts for life. You don't see men subjected to the same thing to nearly the same degree.