I'd argue that it's because (true/hard) AI represents, in many ways, the "final frontier" of scientific research. Not in a literal sense -- they'll always be something else to study. But the notion of creating a thinking machine is, in many ways, the ultimate goal of studying nature and the world around us: to allow us to understand the processes and phenomenon at work well-enough to be able to capture/manipulate/recreate them at will.

This isn't new though -- "thinking machines" have captivated audiences for millenia. See the Antikythera mechanism [1], the Turk [2], and so on. The ability to replicate the capabilities of our own brains is intoxicating -- it finally signals that we, homo sapiens, understand our own minds well-enough to recreate their abilities at will.

[1] https://en.wikipedia.org/wiki/Antikythera_mechanism [2] https://en.wikipedia.org/wiki/The_Turk