This is because it doesn't work in the same way as most traditional templating, where your images get added to the package and are then published by another TBB, which I guess is what you were expecting when you tried to use the Image Resizer.
DD4T 2's Generate dynamic component TBB (which actually just calls the BaseComponentTemplate) publishes multimedia components using it's BinaryPublisher as it builds the dynamic component for serialisation. This is (partly) because it also includes additional information such as width, height and file size in the serialised data.
In other words, by the time your Image Resizer TBB gets to do it's magic, it's too late... The image has already been published in a previous step.
Usually, in DD4T based solutions, a delivery side image re-sizing system is employed, such as DD4T's own or SDL Web's Contextual Image Delivery, which negates the requirement to republish data if your templates change and consequently require a different sized image. It also helps if you need to serve different sized images for a responsive and/or adaptive website. Based on previous experience I would definitely recommend this approach and, given that the DD4T team does not supply a templated solution for re-sizing, I think it's pretty clear that they would recommend it also.
If you really want to resize your images during publishing, I have previously written extensions to DD4T's templating libraries, which publish re-sized versions of a component's images and "inject" the published URLs as additional metadata on the serialised multimedia components. If you only need to re-size the image once, then I guess you could do something similar but just replace the published URL, width, height and file size etc.