One scene explains where Snoke was during the OT, where he got his power/money, why he dresses in an ostentatious glittering robe (he’s a wealthy crimelord, not a sith lord), where he got obsessed with the Solo family, and thematically wraps up his role in the cycle of revenge.
This isn’t the MCU. You shouldn’t have to watch spinoff material to understand everything.
That said, that idea does sound kinda nice.
They also could’ve done a backstory for Snoke in TLJ in the “second lesson” scene: make minor tweaks to some of Luke’s dialogue, suggest that Luke had met Snoke and they re-formed the Jedi Order, Snoke saw the power within Ben and so he corrupted him and betrayed Luke.
That one too.
Really, Snoke’s backstory isn’t that important. It’d be nice to have, though.