Why can't I select all of the text in AI that's probably not text?

The text is converted to outlines so that you don't have to have the font. 

If you open the Layers panel (Window > Layers), is there a layer that contains all the text sublayers? If so, then you should be able click to the right of the circle (or the target circle itself) that is to the right of the layer name to select its contents and delete it. If there is other content in sublayers in the layer that you want to keep, you can instead Shift + select the sublayers and click the trashcan at the bottom of the Layers panel to delete them.

Generally, that happens when a .ai file has passed through Acrobat .pdf translation at some point. Or the type has been rendered as outlines, essentially drawings of type characters, so the file can be printed/displayed without the original font installed.

While Illustrator and page layout programs like InDesign let you set a contiguous block of text — and highlight it all or any part of it as such — if that file transitions with a .pdf format it will be broken up into phrases/words/individual letters. It's a pain, but it's a known problem. The best way to work with that type is to use your Selection/Black Arrow tool to drag-select all the type, and unfortunately, any graphic elements around it, then use the Shift key to de-select the elements you don't want. Once you have only the type characters selected, deleting them is easy. Press the Delete key and they're gone. If you miss the first time, use the Edit>Undo menu command to return to the baseline, then refine your selection to get exactly what you want from the file.

With type rendered as outlines, the process is much the same. Selecting the character drawings only with your Selection/Black Arrow tool, then dispatching them with the Delete key.

If you want to edit that type, you're flat out of luck with type that's been rendered as outlines. With type characters that have been broken up with PDF rendering, you may be able to use the Edit>Cut menu command, get your Type tool to drag/create a text frame, then use the Edit>Paste menu command to paste the text inside the new text frame. But it will blow the leading values, perhaps a bunch of the other sophisticated type tricks applied to the text, and if you don't have the font used installed on your system, likely the application of that font to the text. You'll have to recreate everything that's lost with that text on your own.

Wish I had a better answer for you, but that's the truthful one.

Randy