No more or less environmentally damaging than anything else manufactured on the other side of the world.
Some bikes may be air-freighted to us but I'd be surprised if most don't arrive at Felixstowe, Immingham or similar in a sea freighted container.
Of course we could braze together bike frames - we do - it just costs much more than TIG welding. We could make carbon fibre frames here, but it costs more. It's us, the buyers of bikes, who push for low prices and at present that means far-eastern manufacture.
The economics of manufacturing remotely and shipping goods thousands of miles isn't going to change soon, and the natural environment and its resources will go on being accounted for as of no value for a long time yet, so don't expect the situation to change, it's a capitalist world and it's going to stay that way.