Why is the employment act so complicated?

I find that Singapore's employment act rather strange as managers or executives are not covered by any kind of employment act. Below is the act which I found in MOM's website.

The Employment Act covers every employee (regardless of nationality) who is under a contract of service with an employer, except:

1. Any person employed in a managerial or executive position 
2. Any seaman; 
3. Any domestic worker; and 
4. Any person employed by a Statutory Board or the Government.

Part IV of the Act, which provides for rest days, hours of work and other conditions of service, applies only to:

1. Workmen earning not more than $4,500 basic monthly salaries and 
2. Employees earning not more than $2,000 basic monthly salaries.

 
Based on the above act, it seems that many Singaporeans are not covered at all by the employment act as most of the jobs that we take are classified under the "Manager or Executive" section. My question is why can't a basic set of rules be applicable to all employees under the employment act.

Manager or executives do also need help if the terms of the employment is not fair. One of the tricks of trade in Singapore is to hire someone that fulfils the requirement of "Manager or Executive" but pay them peanuts. These employees are then exploited and could not find resolution under the employment act as it specifically excludes them.

I feel that the standard set of rules should cover the terms in the employment contract as not all of us are able to understand the employment contract that we sign. Some employers do take advantage of this loophole and put in unreasonable terms which we are bounded. For example, working for free if you do not meet certain KPIs.

Although Singapore is pro-business but this is taking a bit too far. Is that fair? Does the government thinks that "Manager or Executives" do not need rights?