This is not a matter of “importance”, our matchmaking has no region preference built-in. The matchmaking happens in two stages-
Stage 1 10 players are selected according to variety of factors - ranks, IR, search duration
Stage 2 For these 10 players the best server location is chosen to give best possible ping provided its <110ms. Important: only pings are factored for calculating the best server, nothing else.
Now, whenever there is a person from SEA (other than India), the chances of the server being SG are high. This is because of the way ISPs have setup routing - Indians ping good to SG compared to how SEA folks ping to Indian locations (this is because most international websites in Asia are hosted in SG so Indian ISPs optimize for that).