How I know the reason! See my story below:
Today, I took bus service 51 to Bugis, when the bus was somehere
near Eunos, a bus ticketing inspector come on the bus and check on
everyone, well, this is his duty and I passed my ez-link card to
him without any question.
After he finised his job, he dropped off and within 3 bus stop, now
the bus is near Kallang and ICA building, another bus ticketing
officer came on the bus.
When it was my turn, I asked him why within such a short distance,
there is 2 inspection, he gave me a f***ing face and told me that
they have the right to check as many times as they want per bus
trip, meaning Starting Point to Ending Point.
I feel it is unfair and refused to pass my card to him, he threaten
me to call the police and asked me to leave the bus at once, as he
said that he was the "king" in the bus. 
Well, I have to rush to work and left the bus, walk 3 bus stops
before reaching my work place.
Here is few questions that I want to bring up,
1) Is SBS worry that no one want to pay bus fare after
itsincreasing and their profit will drop and they are unable to
answer to their shareholders 
2) Is bus ticketing really a "king", if so, is SBS services moving
backward just because there is not competitors, like Singtel in the
past
3) By increaing the number of ticketing officers, cost will
increase for SBS and in the end we have to pay more for someone
keep checking on us on our per bus trip
