Viacom probably feels there is a sufficient lack of content or lack of value to have these as attractive stand-alone channels that would appeal to MVPD's, and it is always a fight to get new channels with little or old content onto an MVPD. These channels overnight content may not be worth the fight in Viacom's opinion. Also, if they were stand-alone channel, that would likely require purchase of additional content (just old repeat shows most likely) that drive up the cost of offering these as stand-alone.
Further, the daytime scheduling of the content on these channels (already on almost all MVPD's at lower subscription levels) can be used as lead-ins to the overnight content and may result in greater viewership (making more money) than if these overnight content channels were left to draw viewers on their own 24/7, especially with content that has been proven to be, especially Adult Swim, niche programming and profitable overnight, but perhaps not so in other far more competitive hours and not necessarily mass appealing, at least here in the US where we have far TOO MANY channels as it is, and most not worth a $1 to watch and pay for.
Because both of these channels daytime content was and still is aimed at children and teens, that audience is nearly completely lost during the overnight hours, or, in other words, advertisers aren't going to spend a lot of money to reach an audience who are sent to bedtime and asleep overnight. So, how to make money on kids programming overnight? Offer programming for adults who are awake during those hours. Now that makes money.
In the case of Disney's channels aimed at kids, Disney too has a dearth of advertisers overnight, but offering adult oriented content during overnight hours would hurt the Disney brand. So, instead, Disney airs repeats of its older TV series, and although Disney channels, too, have a dearth of advertisers overnight, Disney uses the commercial breaks to exclusively promote Disney products such as its other TV programming, coming movies from one of its studios (lots of Star Wars movie promos, too), stage musicals including stage presentations on tour, its theme parks, and ship cruise properties, often leveraging its Disney Channel and XD talent (popular young actors and performers on its Disney owned TV shows) who promote and participate in the stage shows or its ship cruise events. In other words, Disney being that largest diversified media monster company (Comcast the largest media company by revenue) has LOTS of properties that it can advertise as "cross promotions" and Disney loves advertising itself and printing money, in fact, Disney "cross promotion" is abundant outside of late night, but not necessarily exclusive as it is overnight. By early morning of 6AM eastern, the animated programming aimed at very young children airs until the later hours when its more profitable programming aimed at older children and adolescents airs well into the late night.
That was more than I thought I would write.