It looks like it might be a licensing conflict. As far as I can tell, the rights to the characters have reverted to Jay Ward’s estate, which is currently being run by his family. But the broadcast rights to the original show is owned by General Mills.
My understanding is Jay Ward Productions can license the characters for new productions. (Which they did with Universal to make some movies.) But they can’t authorize the use of the original show.
General Mills can license the broadcast of the original episodes but apparently it hasn’t done so since 1998.
As far as I can tell, there are no issues with music rights.
Both of those DVD sets were apparently issued by Universal (if the Amazon listings are accurate in that regard), so either the broadcast rights are separated from the home video rights, or General Mills gave a license to Universal for the DVDs.
At the risk of being repetitive, if you look at the box pictured in the RB2 Amazon listing it clearly states 18 DVDs and an appropriate total running time. The textual Amazon description appears to be wrong.
And RB2 includes non-DVD items not included with RB1.
June Foray: Rocky, Natasha Fatale, Nell Fenwick, and most of the other female characters
Bill Scott: Bullwinkle, Dudley Do-Right, Fearless Leader, Mr. Peabody, and others
Veteran voice actor Paul Frees did Boris Badenov, Captain Peachfuzz, Inspector Fenwick, etc. Other voice actors (including Hans Conried, Daws Butler, Walter Tetley, Charlie Ruggles) did certain voices.
William Conrad was the narrator/announcer for a lot of the segments, while Edward Everett Horton was the narrator for Fractured Fairy Tales.
In 1962 Jay Ward and his publicist staged a “Statehood For Moosylvania” publicity stunt/campaign. They leased an island in Minnesota and drove around the country with a petition asking for the island to become the “State of Moosylvania”. After visiting 50 or 60 cities and collecting signatures from fans they drove to Washington D.C. with the petition hoping to present it to President Kennedy.
Unfortunately their timing wasn’t too good, they arrived in the middle of the Cuban Missile Crisis and were turned away.