First of all, the 100 million is only around half the team's budget. The league and the players agreed on using only 51% of total revenue for player's salaries. It is rational to spend all of it firstly because there is no other way to spend it. Secondly, you would make yourself unattractive for potential Free Agents. The side-effect is, that decent players who far from being superstars can make a fortune in mediocre teams. Current examples are Otto Porter for the Bulls or Mike Conley in Memphis.

First of all, the 100 million is only around half the team's budget. The league and the players agreed on using only 51% of total revenue for player's salaries. It is rational to spend all of it firstly because there is no other way to spend it. Secondly, you would make yourself unattractive for potential Free Agents. The side-effect is, that decent players who are far from being superstars can make a fortune in mediocre teams. Current examples are Otto Porter for the Bulls or Mike Conley in Memphis.