That’s because the sim’s built-in flight planner is not capable of understanding all the ARINC procedure legs that LNM does when you create the plan outside the sim.
Additionally, none of the stock Flight Management Systems (i.e., GPS) are capable of understanding and executing them either. The only two FMS that understand most of the procedure leg types are the Working Title CJ4 and the G1000 NXi. So you will always see oddball things like massive course turns instead of a tight leg for example.
The G3000 will be updated to NXi after the latter leaves Early Access and the CJ4 receives the updated treatment. Eventually, Working Title will rip out the sim’s FP logic and replace it with the one inside the NXi so all FMS, Working Title or third party can benefit from full ARINC compatibility.