The common reason given is that Indian cooking involves lots of spices that stain and remain in the kitchen, necessitating either a kitchen overhaul prior to renting to a new tenant, or renting to another Indian family. I understand and am sympathetic towards this reason, having frustratingly burnt-in a few permanent turmeric stains into my work surfaces. But just a little. To be a landlord in Singapore is to be of a financial status that most Singaporeans are not a part of.
And again, I also know it is simply a smoke screen, because these same landlords are also the ones complaining about "all of the Indians in the neighbourhood"! And making variations of the blinding smile joke, bobbing their heads mockingly, wrinkling their noses in disgust at the imagined smell of food or perfumes or incense, complaining about the noise they make, and advising you earnestly to never invest in property in known Indian enclaves.
Thank goodness not everyone is like this, and thank goodness for the enforced racial quotas of government housing.