like others have said, it is about the Noise figure.
a hypothetical example, say you have a length of coax with total attenuation of 10dB, and a LNA with gain of 20dB and noise figure of 2dB.
if you have the coax first, followed by the amp, total gain is 10dB and NF=12dB.
if you have the preamp first, followed by the coax, total gain is 10dB BUT NF is only 2.2dB!!!
so, a difference of 10dB by just placing the pre-amp first in the line, that means, you can pick up aircraft whose signal is 10 times weaker, than if you have the LNA after the coax.
the Noise figure of the first stage is the most important, that is why it is meaningless to have a very expensive attenuator (coax) in front of a LNA. Rather have a LNA followed by a cheaper coax, than the other way round. If you look at some of the better multistage-filtered-LNA’s, you will see the philosophy followed there too.
just Google “cascaded noise figure” to get the formulas and explanations.
The caveat is that in our scenario with amp 1st, followed by long coax/filter combinations, that your LNA must be able to handle large out-of-band signals too, that can be quite challening if you live near a cell-phone tower/airport, etc. in that case you need either an expensive LNA (or one of the bettter filtered LNA’s) followed by the standard chain, or plug your spectrum analyzer to the antenna, capture the signals, and start number crunching, and see what combination gives you the best compromise…. And even then, things can get compromised by RF-noise climbing into the shields of the coax, or very weird issues close to high-power transmitters, like cross-modulation caused by a number of different reasons, but that is a totally different field.