This trade technically fails until 12/15 as Gary Harris can't be traded until then.
Why Orlando Does This
It's pretty obvious to any NBA fan that Orlando needs better guard play. Ant Simons and Paolo would be a force in The East and it gives balance to their roster. They give a few Guards and two 1sts to get an elite guard.
Why Houston Does This
Houston could also benefit from better guard play. They give Jabari Smith (who they've attempted to use as a guard in his time there), to get a true guard in Cole Anthony and get two 1sts to use or move along for more upgrades.
Why Portland Does This
With the rebuild in full swing, the backcourt of the future is Scoot Henderson and Shaedon Sharpe. This leaves Ant Simons as an obvious piece to be moved. There is also a glaring need for a PF of the future in Portland...enter Jabari Smith. After drafting him #3 in 2022, Houston has done very little to utilize the skillset he showed at Auburn. They give Ant Simons to slot in their PF of the future next to Donovan Clingan.
Possible changes
If Houston needs more to make this deal work, more could be sent from Portland (such as Robert Williams). Portland could take a combination of picks and salary to give this trade a green light.