..., of course they do! That is the point of a pilot episode?
Lots people will tune in to a hyped show like Gotham so the initial figures for the 1st pilot episode will be huge. However, once people HAVE seen it and stop watching by the 3-4-5th episode THEN it becomes the viewer retention figure that's all important.
Pilots are important to get a series going but if the figures drop rapidly afterwards then it's Bye Bye!