For landscape photography the advantage of most prime lenses over kit zooms is not the maximum aperture, it is the sharper image it can produce at middle apertures (i.e. f/4-f/8) and better performance in the areas of distortion, vignetting, and chromatic aberration. While you can correct for those in post, you do so at a price of maximum sharpness.

Traditionally a lot of street photography has been done using 35mm lenses and 35mm film. That field of view equates to 23mm with your APS-C cameras. The wider aperture of a prime lens allows shooting earlier in the early morning twilight and deeper into dusk. The image quality concerns mentioned above in relation to landscape photos also apply, although distortion is not generally as big an issue for street photography.

There are also other use cases that will take advantage of the faster aperture, night sky photography being the most obvious. While that might not be a use case that you would ever consider there are many users of such lenses for which that is the primary focus of their photography. Just as you like to do street photography and portraits, those use cases may be ones which others would consider things they might one day do, but never end up actually doing.