actually i wouldn't be surprised that most in sg don't make a lot off their work income, but if you factor in investments and rent, then will be earning a lot more.
Could get $700 - $1k/month off renting a room out, save a lot and invest most of the savings earn another 1k/month.
Just need a job that pays 5.5k (including bonus), if the job pays 4.5k + (3 months bonus), including rent + investment, then will hit that amount liao
Some people are also likely to rely on family money for rent/investments, even with low paying job, are able to earn more in comparison.