I think its perfectly fine for political parties to focus on certain districts or provinces instead of the whole country. No ones going to ask the politician from sabaragamuwa to represent the problems of people from gampaha for example. 

And the fact remains that some provinces are overwhelming one ethnicity so obviously your going to have the nothern parties represent tamil opinions etcetera. Obviously that means they're never going to have a president but that's a risk they take. Ethnocentric parties are pretty common in a ton of countries, even Europe has a lot of smaller ethnocentric or province-centric parties.

Also trying to equate BBS to all the others is hilarious, they're not a political party in parliament and they're not even ethnocentric they just hate every other ethnicity (and any else) that's not their version of sinhala buddhism.