Because that's the way democratic legislatures work. If your law does not get approved, it means there's something in it that a majority does not like. Therefor

Because that's the way democratic legislatures work. If your law does not get approved, it means there's something in it that a majority does not like. Therefore there is an iterative process, actually in two parts, the first being amendments added as the bill is read, the second being re-submission of a modified version that it is hoped will be more appealling. The fact that something is submitted again and again with various modifications each time is not unusual, it is just government working as intended, making sure the things that become laws are, in fact, things we want to become laws.