The Star's azipods are having thrust bearings problems, and need to be replaced.
As any good auto mechanic will tell you,
"you can pay me now or pay me more later."
NCL has made a wise decision to repair or replace the bearings at the earliest possible time that they could schedule a drydock with the replacemnt parts in hand.
Waiting onto a futre drydock risks destroying the azipods, which cost significanly more than the bearings in question.
Meanwhile, reducing the Star's speed to minimize future damage to the azipods is a sound policy.
Would you rather be stranded 100 miles out from your first port of call when the azipods completely fails if NCL continued sailing the Star at higher speeds, or would you rather make all the ports on the slower revised itinerary of the cruise, including returning to LA on time?
NCL subsituted two ports for the two ports you're missing from the initial itinerary. You should be thanking your lucky stars that's what they did. NCL could have, per the cruise contract, cancelled the two ports without any substitution.
And NCL added $100 per cabin on board credits on top of that, which they don't have to do. $100 at today's prices aboard, is approximately 20 beers. Sufficently large enough for you to wash away your tears and disappointment.
Many are happy NCL dropped Acapulco from the itinerary, as the cruise tour vendors and street people are very aggressive.
I know your pain that your cruise isn't what you expected it to be. But mechanical problems aboard any ship need to be addressed as quickly as pratical. You can either make lemonade with lemons, or make faces as you eat the lemons raw.
It's up to you which you would rather do. Go on your cruise, change your plans some, and enjoy the two new ports as much as you can that were added to your itinerary and have fun!