They wanted to open in April. Then May. Then June. But the Minions water ride just wasn't ready. And not just its aesthetics. We're not sure exactly what was causing the delays, but TMs confirmed it had issues.
Universal was in a tough spot. The summer was slipping away. School had been out for 40 days by July 1. So they made the choice to open with some bare walls.
Also, day one's shade was miles ahead of what we encountered during previews. I doubt those updates were due to guest feedback. Everyone knew umbrellas were needed, including the TMs on the ground. They were suffering more than guests were. Visitors were never far from AC, while they had to take pics of families hugging SpongeBob without any sun protection. They all have umbrellas now.
I do hope that guest feedback influences them to build indoor rides exclusively in the expansion lands. And perhaps throw up some canopies over a few existing rides, especially in Bikini Bottom.