These people rent a villa or flat consisting of 4-5 rooms and then share it with the others to live in. In this situation, sure they will look for the people who are the same culture and speak the same language.
For example if they will bring me, I will be in trouble and also them. so better to have the same nationalities.

Explanation for why only Indian or Filipino....We know here the majority of expatriate is Indian (Mostly Keralite) or Filipino. It is obvious you will see much more ads from them.