Because if things get to the point that you think you’re going to need to run a level 2 diagnostic, then you might as well just skip straight to the level 1. Because if you don’t, you probably still aren’t going to find what you were looking for (or at best incomplete data), so you’ll still have to waste even more time running the level 1 anyway.
Otherwise the level 3 will suffice. It’s going to catch the large majority of issues just fine.
Because if things get to the point that you think you’re going to need to run a level 2 diagnostic, then you might as well just skip straight to the level 1. Because if you don’t, you probably still aren’t going to find what you were looking for (or at best incomplete data), so you’ll still have to waste even more time running the level 1 anyway.
Otherwise the level 3 will suffice. It’s going to catch the large majority of issues just fine.