I love it and find it very good quality.
That yellowing is likely from manus detritus, i.e. dirty hands.
So, being less grubby would prevent yellowing.
Mine been outside all day all summer long and hasn’t yellowed. Cue the jokes about British summer.
Seriously, oils from skin will discolour all plastics rapidly, which is why most plastics that are touched regularly, i.e. throttle on a bike, are black.