No insider information, but I worked on a similar guest facing value at a different company where we deliberately "lied" to our customers about a value. So, I have some theories:
For why it doesn't update more often
- people don't want to get in line, just to see the wait time drop 2 mins after they got in line
- people don't want to see a 20 min line, run from the other side of the park just to see it at 30
- Any of the physical signs remaining, no need to wear out the components faster than needed
- If you already have a built-in buffer and the actual predicted time is still less than it, what change it?
For why it isn't more accurate
- Guests feel like they "win" when actual time is less than posted
- Increased LLSP/LLMP sales
- Steers guests to less popular rides to better utilize park ride capacity
- Can steer guests away from area if lines in one area of the park looks crowded
- Get people to balk at rides at the end of the night to close them down earlier.
I'm sure others can think of more reasons, but these are just some of them.