It's not though, it also affects those who live anywhere within the M25, which would be generous to call "London", particularly the more neglected parts, in public transport terms in the south and south-east.
What parts are you talking about? Most areas in the m25 is part of a London Borough. Watford isn't but has decent rail connections and has tfl bus routes ending there.
There are some parts of rural Enfield and Barnet which aren't so great for public transport connections admittedly.
I mean, pick basically anywhere east of centre, or anywhere served by Southern or Southeastern, some of the worst rail operators, or anywhere more than ~20 minutes walk from a station. Being a London borough doesn't mean much in some parts, other than being subject to the will of London, despite a very different landscape.
I live in an area served by Southeastern and have plenty of non-Southeastern transport options.
So your conclusion is not "we should invest in transit to those neglected areas", it's "let's subsidise driving everywhere". Interesting.