Though it never gives any indication, PokemonDB's egg move pages only include data for the most recently released game that includes the Pokemon in question. In this case, the most recent game to include Vileplume is BD/SP. So, you are seeing compatible parents for Strength Sap on Vileplume for BD/SP only, which means Morelull and Shiinotic are not listed (because they're not in BD/SP).
This issue affects all egg move pages on PokemonDB, which is unfortunate. We've asked previously for a game picker to be added (as the data clearly exists already, when you look at the moves via the main Pokedex pages). In the meantime, the most complete and most granular egg compatibility info comes from Bulbapedia.