In addition to doing live commercials (banned now since the 70's) local kiddie show hosts also served a purpose as "traffic cops." They tied up the loose ends and made the show run on time. The old cartoons everyone loves (Warner, Walter Lantz, Terrytoons, etc.) and other stuff (Our Gang, Laurel & Hardy, 3 Stooges) were originally made for showing in movie theatres. In theatres it doesn't particularly matter if a cartoon runs 6:41 or 7:19, but on TV it sure does. The random lengths of these items might make them difficult to use now without live hosts. When I was a kid, one local TV station ran cartoons without a host as a filler; they simply spliced a half hour 16mm reel together, and when time ran out, just switched off the last cartoon in the middle! (Come to think of it, most of this stuff was syndicated on 16mm film; how many stations even have the equipment any more?)
There is also, frankly, disinterest on the part of the owners of these properties (Disney and Warner excepted.) The son of a friend was working for Viacom a few years ago and asked why they weren't doing anything with the Terrytoons (Mighty Mouse, Heckle and Jeckle) and their response amounted to "what does anyone want with that old crap?" 20 years ago there was a multitude of syndicators large and small, all out there selling their shows; good, bad, indifferent, or lousy. Now so much material is concentrated in so few hands that the big dogs in the biz are mostly concerned with selling only what's hot; the rest can rot in the vaults, who cares?
Some shows have even been deliberately destroyed; as Hallmark Cards did to most of Filmation's inventory. (The versions Classic Media have are PAL system transfers at 25 fps and run about 5% too fast on US TV; when they wanted to do NTSC transfers, Hallmark told them all the original films had been junked as the company had placed no value in them. (Hallmark came close to doing the same thing to the original Laurel & Hardy negatives, only a third-party intervention stopped them. When you care enough...)