I am disappointed by that too... It really would add more of a challenge to the season/franchise mode if there were frequent injuries... This feature has never worked properly.
In real life, injuries occur mostly between games, such as during practice, or they are just a result of constant wear and tear. In games, they usually occur on accident, not as a result of a hard foul.
Another thing that bothered me about injuries in Live is that they always resulted in a flagrant foul, and vice versa.
Live should do an injury check every day during the season, and also during the off-season. There should be random injuries during the game while players are jumping for shots or rebounds, or executing special moves like spins and crossovers. Imagine AI actually "breaking" someone's ankles on a crossover. lol
Still, since Live is the only PC hoops game out there, I will buy it and play the hell out of it.