Probably because the service court is necessary for the operation of the stores, restaurants and entertainment venues for things like deliveries and trash service.
As for AMC, they just reduced the capacity by changing a bunch of theatres to dine in theatres. If they wanted IMAX, they'd convert one of the two big theatres, they wouldn't add anything. They have the "ETX" auditorium which is basically private label IMAX with better sound (Dolby Atmos vs. the shrill and loud IMAX sound).
Also, I don't think that service court is close to big enough to add an IMAX theatre. Look at how much real estate the large balcony auditoriums take up on an aerial photo. One of them is essentially from the wall with the big AMC sign to the white line in the roof near the circular structure. You can easily tell because the ceiling in those two is much higher than the rest of the complex (with the exception of the lobby on that side that is the same height).