Chris Paul to the Lakers being veto'd was because the league, at the time, collectively owned the Hornets. So it made a little bit of sense for owners like Dan Gilbert and Mark Cuban (who, effectively, were 1/30th owners of the Hornets at the time) to say they don't approve of the trade. It was a stupid, one-off situation, and not something you can apply to future transactions.
To your second point, nothing is stopping Paul George or LeBron from taking whatever money they want, and nothing should. You want the NBA to step in and tell LeBron he needs to take more money? Why would they care? The NBA is run by the owners, why would they want players to take MORE money? What is really causing the issues you are describing are max contracts. The league has already artificially put a ceiling on how much players can make. IF they removed this, and all of a sudden KD had to decide between taking a hair less than the max from GSW, or taking $50 million a year from LA or Philly, that makes the decision a little more difficult, wouldn't you say? As it stands now, the league has basically said that LeBron James and Paul George are essentially worth the same, which is ridiculous. IF all teams are offering the exact same amount of money, why would a player choose to go to a mediocre or outright bad team over a contender?