I am trying to use the frame tool in illustrator. I want to create a layout of empty frames and fill them with images via drag and drop like you can do in Indesign... but the frame tool doesn't seem to exist in Illustrator? That can't be true surely?
There is no frame tool in Illustrator. You can use a clipping mask if you want to crop an image non-destructively. Or, select the image and click the Crop Image button on the Properties panel to remove pixels. To create a clipping mask, select the image and click the mask button on the Properties panel. This creates an invisible rectangle the same size as the image, that will crop the image when you change its size. You can change the size of the clipping mask rectangle in the properties panel. Make sure the edit clipping path button is turned on at the top of the properties panel, then you can change the size numerically in the fields below, or use the selection tool to drag the bounding box handles around the image.
While "page layout" can be done in Illustrator's object-based interface, that was never the primary thrust of the application's design onus, so many of InDesign's layout-purposed features are not paralleled in Illustrator.
It sounds like you do have some familiarity with InDesign so is there some reason why you want to do this in Illustrator rather than it a program that is designed for page layout? Each of the programs offered through Creative Cloud has a primary reason for existing. Illustrator is a drawing program that has some layout capabilities. InDesign is a page layout program with some drawing tools. To expect that all of one program's capabilities will exist in the other is just not how it all works.