Simple 2 Servo Synch
The Arduino Servo class is intended to accept positive values only, in the range of 0-180.

In addition to reversing the values for one servo by subtracting from 90, your code is also negating the values by multiplying by negative one.

That results in an invalid argument to the Servo function.  It's unclear exactly what happens, but likely possibilities include an invalid pulse, or no pulse at all.

At the end of your for loop, you subtract 90 from 90 producing zero, and invert it to still zero.  Zero is a valid input to the Servo function, so a valid output is produced and the "reversed" servo finally has a position it can seek to.