Because it’s a sub-Cues group? Interchangeable with current stuff (unlike Cues), and so addresses concerns of those who either don’t want/need the increased durability that Cues brings, or don’t want to pay the entry price to that set up as it’s effectively a whole new group, whereas Essa parts can be used in existing 8 speed set ups.
Essa- entry level 8 speed compatible with existing parts.
Cues – 9/10/11 speed set ups with some cross compatibility but not backwards compatibility, and with focus on durability for some MTB riders and E-MTB riders.
SLX upwards – 12 speed Hyperglide+ with focus on shift speed and performance.
Makes sense for the different types of rider out there.