Paul Corfield wrote

recognised that TfL fare levels are so far below what is charged
elsewhere that commercial bus companies cannot afford to charge them
on a wholesale basis although some do what Metroline are now offering
which is charge a cash fare which gives them money in the bank today
rather than a lot less money in the bank at some time in the future.

You'll note that where TfL do run "over the border" that there are no
competing parallel commercial routes - it would be commercial
suicide.
This is one reason why Ensign won't run into Greater London from
Lakeside or Grays - they leave it to TfL routes 370 and 372 - and the
punters have to change buses rather than have a through route which
might be the logical thing to provide.

as to competing parallel commercial routes

Is your terminology quite right ?

Thus from Kingston to Staines TfL 216 and Abellio Surrey's 458 (once
218) are 'parallel' but have no other points in common. I assume
everyone who pays prefers £1.35 to £3.90 for the full journey.

Abellio 461 (Kingston-Molesey-St Peters H) in fact a commercial route,
again I assume everyone who pays prefers £1.35 on the TfL 411 to £2.40
for the Kingston-West Molesey journey

Kingston-Esher has TFL K3 via Claygate which takes 35 minutes, 15
minutes longer than the Abellio 458/459 at £2.40

--
Mike D