@Pearl12 think it was just for faction diversity (yep there it is again). I think at first, it was changed, as @Nari said, to be a short range mavor. It was half price, ~110k mass, and had about 8-10km range. Since no other faction had a 'cheap game ender', cybran had an uncontested win condition on 10km maps. It also overlapped with t3 arty at ~70k mass and outperformed. It was also useless on 20km maps, due to said short range, giving cybran no game ender on it.
But anyway, cybran needed a game ender different from mavor, and since scathis is a rapid fire artillery, they exaggerated what made it different to make it even more different, i.e. loads more aoe, very low accuracy, very low damage per shot (compared to mavor); this matched the style of cybrans other arties, treb and disruptor. I think the volley idea was just something someone came up with and it stuck.
I personally think it looks dumb for the canon to spin so fast. If they shot cluster projectiles instead, like how their bomber shoots 6 bombs, then it would look way less stupid and not like a modded unit. This change would even keep it's shot per volley the same. Also, it would split early unlike the aoen rapid fire.