Why is there a fixed amount of test amounts?

Yes, I found this information but it doesn't show or tell me how to do this. The info I found doesn't give any detail. Additional Attempts: Set to 5 by default. Type a number between 0 and 99 to indicate how many times the student can re-take the test. The student’s mark will be the score of the most recent attempt. Note: If Allow Retesting is checked and 0 is entered here, the number of attempts is unlimited. The number of test attempts left is not displayed in the project.

I'm not sure I follow, but to be more specific, each project has a publishing profile associated with it. If it has not been changed, then it is the "default" profile. Which publishing profile the project uses it set in the project properties of the project. To change a publishing profile you can access it from the Application menu (the hamburger icon in the upper left) and select Publish -> Publishing profiles. Select the desired publishing profile and choose to edit it. Under the testing section set the Test Attempts to 0 and allow retesting. This will then stop displaying the number of remaining attempts in the project automatically and make it unlimited.

Ah yes, publishing profiles can be locked. If locked the user who locked it would need to unlock it to enable it to be edited.