> Lightly is incredibly slow
Its relative! Sitting on a couch and watching the pixel move from the sun to the earth for 8 minutes feels incredibly slow but if you are actually traveling in a light speed aircraft then it won’t feel that slow.
I believe the OP was referring to relativity - the closer to the speed of light you get the slower time appears to tick. So if you could travel at light speed you'd arrive at your destination immediately from your reference frame, but much slower from another person's.
1) it's better for the plot and drama to have travel time. FTL in fiction is always analagous to some known terrestrial form of travel (usually ships and boats) and the limitations and parameters of FTL in a fictional universe shape the narrative in necessary ways.
2) it's assumed within the framework of the fictional universe that time dilation isn't taking place because the actual travel is occurring within an external frame of reference like "hyperspace" or a "warp field."
If you were actually traveling at the speed of light it wouldn't feel like anything at all! Photons don't 'experience' time—any length trip would be instantaneous from the traveler's point of view.