Prepare for the post-Kevin Durant era
There's a chance that Kevin Durant could ditch the Suns soon. Although it's unsure when that will happen, there's a lingering question on Durant's loyalty. Developing the player that the team will draft this year might be a significant key in the long run.
If the Suns get to develop the prospect while they're under their rookie contract, the trade value for the player could increase. Now, trading Durant (if it comes to that situation) might not be a serious problem in the future. The front office will have an advantage down the line when it comes to getting something in return for KD with their 22nd pick.
Getting another star to help Devin Booker once Durant decides to leave the Suns will be important. The front office will benefit if they keep the pick this year and draft a promising prospect to be part of a potential package in the future.