1) There is no lockdown / shelter-in-place / quarantine in Singapore. Normal residents can go about their daily lives as usual, with a few restrictions for crowd control and a lot of temperature checks.
2) Being stuck in a hotel room for two weeks, no matter how luxurious, is a lot less pleasant than being able to carry on with your life as usual.
3) This is done because returnees from the US and UK pose a high risk to Singaporean, and if they are quarantined at home with family that risks spreading it to family and then into society.
Writing this from a cafe by the river in Singapore, not locked into my apt. It's a beautiful day today with lots of people walking around.