Splash Island was added in 2015 along with a visual refresh of that side of the waterpark.
Good point, but Splash Island was an exceedingly modest addition, and it's so small that it could conceivably be moved. Plus, Splash Island was literally
the last "major" addition to the north side of the water park. Since then, they've demolished Tornado, removed the little market they also added in the middle of the lazy river in 2015, and gutted the old restaurant by the north side changing rooms. The only other investment I can think of into that area was that Freestylin' was repainted sometime around 2017.
Meanwhile, during that same time period, investments into the south side of Soak City have included Hurricane Heights, the Beach Street dining area, an updated Sharky's restaurant, a repainted Pipeline Peak, a new water play feature by Pipeline Peak, Coconut Shores (Lighthouse Landing plus Sand Dune Lagoon), a new cabana area, and an updated entrance area around Tidal Wave Bay.
That'll make 2015 a full decade since any noteworthy investment into the area, along with a decade of steady removals, while the south side has been plussed up significantly. I don't know what the park or Six Flags has planned for the future of the north side of Soak City, but there's a clear pattern that suggests to me that they've planned (at least at one point) for the future of Soak City to all be behind Racer 75.