Here is the point: we have discovered that simultaneity differs for people depending on their relative movement and the next thing we do is to go on to use a measurement technique that precisely makes use of the concept of simultaneity?. Worse yet, we even stop using the technique that we were already using to measure length which involved no simultaneity for the stationary train even though it can be perfectly validly extended to moving trains. In the stationary case, George walks past the front (or the back) of the train and as he passes the front (or back) he attaches the tape measure to the front (or back) of the train and reads of the value as he passes the back (or front) of the train. If the train is moving (assume towards him) he can carry out the identical measurement as he walks past the front (or the back) of train as he passes the front (or back) he attaches the tape measure to the front (or back) of the train and reads of the value as he passes the back (or front) of the train. If George is feeling lazy he can even stand still whilst the train passes him. Does anyone doubt that the value he reads off his identical whether the train is moving or not? From a physics viewpoint it simply does not make sense to replace what we believe is a perfectly good measurement technique which gives the same value whether the train is moving or not with respect to the measurer with a different technique that does not. There is no reason, as a thought experiment , that if we have clocks and rods that we cannot also have measuring tapes (even if they are hundreds of light years long). That measurement techniques involving relativity of simultaneity gives weird results is clear but why should we ascribe these results to actual properties of space when we can simply use the same measurement technique as when the train is stationary. A technique that is invariant to movement such as the measuring tape.

You can not measure a moving train attaching a measuring tape at the ends of the train when its front and its back are passing by you. In case you use that technique, the measuring tape will be moving with respect to you so, the tape itself will suffer lenght contraction as well as the train. It is true, the reading of the measuring tape in motion would be the same than the reading when you measure the train at rest because in both cases the tape is at rest with respect the train. With the moving train, the tape would be also moving with respect to you, so 1 cm of the moving tape will be shorter than 1 cm of a tape at rest. You would be measuring the rest lengh in both cases and this is not what the experiment is trying to do

Levels of complexity required to calculate planetary and moon factors to allow travel of robot observers.