Because there is nothing better than a society where everything can be had at the whim of a machine, hard work of any sort is only pursued as idle playtime or hobby, creative arts have stagnated as evidenced that no one can reference more than one person/alien prior to naming dudes from a thousand plus years in the past like Yeats, Kipling and other bygone dead guys, and the only way to stimulate the mind is to hurl yourself out into the endless void of space in what amount to highly inefficient motor vehicles.
Seriously, we've seen episodes that have proven transporter technology can beam people from place to place at light speed, humans can be downloaded onto teleporter backups, and warp engines are capable of Warp 9. The effective thing to do would be to create a tiny flying transporter that could beam some people down to a planet, explore, beam them back into data and return. Starfleet is the future of LARPERS and the SCA.
Not that it would matter anyway.
An alien race would visit earth and ponder upon the remains of billions in these electronic boxes. Because seriously- Holodeck? I can have a real universe at my fingertips without ever leaving a 10x10 room ever again? Pffft, who'd want to explore space when you could explore everything.