I hate to say this, but you are stereotyping all those services
with Citaros as services with poor demand. That is absolutely not
true. Go and look at the airport services using Citaros, they are
always packed from the airport almost all day (10pm at night it is
still packed) unless there is bunching. Regardless of whether a KUB
or Citaro comes.
Constant Citaros on 43 is just because HGDEP is using them as
any other spare bus to go on its services, just like any other HG
SP Mk3/Mk4s. Nothing to do with how poor the demand is
please.
I would say that HGDEP (or rather SBST) would rather deploy
their new buses onto those long haul and popular high demand routes
(eg. 27, 43, 105, 163 etc). Whereas those short haul and low demand
routes (eg. 11, 103, 115 etc) gets only those MK4s in their fleet.
Even services like 74, 89, 107, 153 and 159 till now had not even
get any new buses at all. Sometimes it might be due to
favoritism...
To me 43 is considered a high demand route and it also serves as
a subsidiary to 70/70M along Upp Paya Lebar and YCK road corridors.
In fact 43 also deserves new buses too based on its long haul
route, rather than sticking to its former MK3 fleet without any
upgrades. Notice the crowds always come in around Serangoon MRT
areas.
Same goes to SMRT. Those popular routes like 190, 851, 961, 963
etc keeps getting the new buses. Whereas the unpopular ones like
178, 975, 980 etc gets only the secondary bus models.