Insert mode is not the mode for editing text.

It is a mode for editing text, because both normal and insert modes are modes for editing text.

Insert mode, however, is the mode for inserting new/raw text directly from the keyboard (as opposed to, e.g., from a register or a file).

Thus, you will only be in insert mode when you are actually typing in inserting (raw) text directly. For almost every other editing operation, normal mode is where you will be. Once you grok this you will realize that, the bulk of most editing sessions is not insert mode, and you actually spend most of your time in normal mode, just dipping into insert mode to add text and then dipping out again.

Insert mode is thus like the passing lane on the highway. Just like you are should only be in the passing lane when you are actually passing other vehicles, you should only be in insert mode when you are inserting text.

Some snapshots from my own learning experiences here and here.