I’ve also been in touch with Jayne – she is right in that the maintenance, siting, planning applications etc. are the responsibility of TfL. However it is interesting exploring reasons why specific docks (in places where they would be handy) haven’t been implemented and the general feel I think is is more to do with cost on TfL’s side than resistance from Westminster Council. TfL have a limited budget for the scheme and this means they will tend towards cost effective installations than necessarily where they would be most useful.
I’d love someone from TfL to jump in and give a different perspective