A general manager's primary objective, no matter what he may say, is to keep his job. GMs typically make $300,000 or $400,000 a year at a minimum, with several earning a million or more. The job also carries tremendous authority and, within a small circle of people, prestige. It is not an easy job, and it can be a 24/7 job, but given the money and perks, it's one that current holders don't want to lose.
The problem is that the best way to keep a GM job when you know you're in danger of losing it is to produce results in the short term, sometimes in the very short term. This idea of trading a dollar in the future for 10 cents in the present often manifests itself in moves like trading prospects or young players for "proven" veterans, signing well-known free agents whose name value exceeds their on-field value and back-loading deals to maximize disposable payroll in the current year without regard to the payroll consequences for future years.
At times, this aligns itself well with the best interests of the organization as most baseball team owners are in the business to make money, with a small number in the business to win; most economists agree that the best way to increase team revenues is to win more games. But most organizations with GMs who are on the verge of a firing are in that situation because of more fundamental and often systemic problems like poor scouting, inability to develop players or the most fundamental problem of all -- insufficient talent. For those teams, a baseball strategy built around winning more games this year, this month or this week is wrong. Trading away young talent, eliminating long-term payroll flexibility and alienating a portion of the fan base can set the team back several years.