Thanks, Robb!
I think what characters or properties were given their own titles was more complicated than just Dell Comics (the distributor) wanting to make a profit over their operating costs for a given comic book series (the publisher, Western Publishing, wanted to sell as many books as possible to ensure the best profit over THEIR OWN operating costs, and the character property copyright owners, wanted either to give their animation or live action characters the most public exposure possible, OR actually make a profit providing a cash flow from comic book sales. So, the copyright owner would ask their publisher to suggest to Dell's publications director/manager to start a new comic book series with a new character, or a similarly well known other character of theirs, which was already selling well with its own series.
As you probably know, The Dell/Western Publishing partnership started packaging and re-printing newspaper comics into comic book collection monthly series in 1936, with "The Comics" and "The Funnies". They added "Popular Comics" in 1937. In 1939, they added "Four Color Comics" and an adjunct- related series, "Large Feature Comics". They started a second "large Feature Comics" series in 1941, closing down the first. And started a second "Four Color Comics" series in 1942, closing down the first. But, by 1938 and 1939, several competitor comic book publishers had been adding newly-made specifically for comic books stories, and some had started individual book titles based on popular characters. So Dell/Western used its new "Four Color Comics" and "Large Feature Comics" to handle the new story comic book individual character's books.
"Mickey Mouse", "Bugs Bunny", "Porky Pig", "Donald Duck", "Our Gang", "Andy Panda", "Woody Woodpecker", "Popeye", "Smitty", "Scribbly", "The Gumps", "The Katzenjammer Kids", "Abert & Pogo", "Peanuts", "Little Iodine", "Henry", "Charlie McCarthy", "Raggedy Ann & Andy", "Little Lulu", "Santa Claus Funnies", and so many more titles which later got their own regularly-scheduled own-titled series, all started (ostensibly being tested for marketability) in Dell's "Four Color Comics" and/or Four Color's adjunct "Large Feature Comics".
It is interesting that a few properties whose character was already extremely very popular in other media, but came to Dell long after Dell already had other popular animation, newspaper strip and literature/novel characters having their own titled , numbered series, start out with Dell having been given their own regularly-scheduled, own numbered series from their start. Krazy Kat was one of those. After 5 issues which disappointingly, sold poorly, his title was demoted back to a much less frequent schedule of releases, and moved into the "Four Color Comics" numbering system. "Charley McCarthy Comics" had an even stranger fate, starting in 1947 being tested as a Four Color Comic, selling well in its first 2 years, and being given its own series in 1949, then selling well through issue #7 in 1951, and sales dropping off a lot in 1952, so after issue #9, it was demoted to a more sporadic release schedule back in the Four Color series until early 1954, when his title was dropped altogether. So, it is clear that Four color comics were used as a home for sparsely-scheduled ad-hoc titles Dell wanted to issue for testing for giving their own series, OR to publish on a break-even or small loss basis, to give the company credibility or prestige.