How about a tinfoil hat conspiracy theory?
When nephew fucked the Spurs over in 2018, they never asked for the league to take any legal action, despite having a case for it.
I'm sure they were aware of Clippers/Lakers/whoever else tampering, but took it on the chin without making a mess out of it.
Wemby was 14 at the time and it was already obvious he's going to be the best player of his generation.
Spurs agreed to stay silent in exchange for Wemby and prepared to have the best odds in 2023.
Castle was just regular draft luck.
The league knew about tree planting stuff before Pablo Torre went public and it would give Spurs enough ammunition to destroy nephew and the league's reputation because the league failed to protect them back then.
But the Spurs are and always will be company men, so they agreed on some more compensation in exchange for their silence.
That compensation was Harper with 7% odds.
More than a fair trade for the Spurs that don't want to be involved in any scandal/trial/process, even though they were the damaged party.