In my opinion, long routes and short routes each have their
strengths and weakness. However, as more MRT lines have been built,
long routes may become a thing in the past since taking MRT is way
faster than taking a bus.
For a start, the major weakness of a long route is its demand
throughout the whole route. There may be high demand only at
certain section of the route but in other section, the bus can be
less than 50% loaded with passengers. In addition, there are
few people that will be taking the entire route.
Take 151 for example. The demand comes mainly in the direction
from Hougang to Kent Ridge. It goes up from Jln Toa Payoh all the
way to Bukit Timah. However, in the opposite direction, the demand
for 151 buses can be low. The longer the route, the unprofitable it
becomes if the demand pattern is in this way.