While Winx Club was directed towards those of a younger age, Fate: The Winx Saga is for a more mature audience which likely caused the shift in character relationships. Bloom and Sky's potential romance is much more complicated in the series now that Brandon, Stella's original Winx Club beau, no longer exists. Sky is Stella's ex and it's clear she still harbors some feelings for him by the jealousy she shows towards Bloom.
Musa and Riven are one of the big relationships on Winx Club and while the characters exist in the live-action iteration, they almost never interact. Musa spends the season hiding her relationship with Sam, Terra's brother, from Terra. Although he's still one of Sky's friends/rivals, he almost immediately has a thing for Beatrix.