Why did the Mavs make the trade for KP when the Mavs team were playing close to .500 ball through first half of the season?
The KP trade will put the Mavs in the 2019 draft lottery to hope for their protected 1-5 pick.
Mavs owner Cuban and head coach Carlisle lied about wanting DSJr. The Mavs organization really wanted Frank in the 2017 draft for factual reason of adding defense-depth in the guard rotation for all the high-scoring PG/SG in the western conference that DSJr 2nd season in the West could not match-up against.
DSJr.'s 2nd season performance and work ethic was not up to par for coach Carlisle, nor was in up to par against the Mavs western conference opponents guards.
For 30 minute playing time DSJr. average to get to the foul line once per game being the ball handler, plus the 4 to 5 assist per game never made up for the 2 to 3 turnovers in the 2nd half of each game.
Plus DSJr. poor defense performance vs Harden/CP3/Curry/Klay/Lilliard/McCollum/Westbrook/Paull/and the other young top guards in the West had to be nerve racking for coach Carlisle.

How well will DSJr. do in New York, under coach Fizdale?
Well, coach Fizdale 50 games (10-40 TANK) coaching the Knicks has not improve or develop any player or young-core player on the Knicks roster yet.
DSJr. may feel at home under Fizdale's half-court isolation system without any demands on the defensive-end.
Fizdale has refuse to build a team-ball system by not selecting two guards as a backcourt tandem to lead the (starter/finisher) lineup, nor did Fizdale select a center and PF as the main frontcourt tandem in the starter/finisher lineup throughout the 52 game rotation .. Fizdale change-change lineup and change-change rotation never letting the players get familiar in a certain lineup or rotation.

I thought the Knicks had found their future small-quick play-maker in the un-drafted Alonzo Trier.
I'm still waiting to see the 2nd season Frank & Dotson tandem-up to run the point in a lineup for the Knicks.