Because teleportation is murder. Whatever comes out on the other side may look and act like you, but isn't you, because you're now dead for having been disassembled by the teleporter.

Teleporters are interesting because when you think about it long enough, you realize the person on departure end died.

Then you think about it more, and if the person that comes out the arrival end is an exact replica, down to the atom, and has continuity of thought... if you accept that they died then you kind of also have to accept that the "you" of any given instant is constantly dying and giving way to the "you" of the next instant. That person living that experience at that exact moment will never exist again.

So then you're kinda back to transporters being business as usual again, but with a fun new existential crisis on the side.

Star Trek's transporters and Stargate's Stargates are cloning devices

The real question is why they wouldn't use the transporter buffers effectively as backups for away teams. Have an away team member killed? No problem, rematerialize them from the buffer.

@taladar @dustojnikhummer Why not just let the crew member stay on the ship and just send dozens of copies of them to the planet to overwhelm any danger with sheer numbers?