As others have mentioned, there are more trains running than there are station LEDs, so in central London the LEDs would almost always be on, which didn't look as good.
For the MBTA in Boston we added LEDs in between each station, and even went further and added LEDs for each direction, but with only 4 lines it was much easier to put together - https://www.traintrackr.co.uk/product/mbta4
We're looking into this for London, but making it look good is significantly more complex with the number of lines and large interchange stations.
As others have mentioned, there are more trains running than there are station LEDs, so in central London the LEDs would almost always be on, which didn't look as good.
For the MBTA in Boston we added LEDs in between each station, and even went further and added LEDs for each direction, but with only 4 lines it was much easier to put together - https://www.traintrackr.co.uk/product/mbta4
We're looking into this for London, but making it look good is significantly more complex with the number of lines and large interchange stations.