https://lkyspp.nus.edu.sg/gia/article/singapore's-hidden-hom...
A friend of mine said it was coz they were homeless and the police were aware.
In other countries they'd probably be moved on by police trying to make them some other department's problem. This could be the place where they ended up where they caused the least headache coz they did somewhat blend in.
It wasn't just east coast park either. There were several who slept on benches outside of my HDB in Clementi and Tiong Bahru. They tended to wake up early.
I left ~5 years ago so I'm not going to guarantee they're still there.
I'm pretty sure the HDB void decks still have their fair share of homeless tho.
Police doesn't care just because Sentosa is pretty much desolated at night, so noone complains or sees them.
There are few other places to mention, way far from HDB/condo settlements in order to maintain a nice picture of homelessness absence.