It would certainly be possible for them to abuse their position in this way, but there may be enough counter motivations. Most are already wealthy, so they are

It would certainly be possible for them to abuse their position in this way, but there may be enough counter motivations. Most are already wealthy, so they are not going to be hungry for money. They are also fearful of negative publicity or information that could help a political opponent. Abusing their position to trade stocks could easily end up in an opponent's attack ad.