The problem is that this .blend file is using the “Diffuse BSDF” material type, whereas the glTF exporter (see these docs) expects a Principled BSDF material. You’ll need to change each material as shown below:
In this example I only change a single material; you’ll need to do the same for all of the materials in the dropdown. With just that one updated, you can see one of the textures on https://gltf-viewer.donmccurdy.com/ already:
