다 can only be "DA",
so to say "DOT", we need "닷", instead of 닻 or 닽.
You could say 닽 or 닻, but it's more complicated, while the pronunciation is the same. So for economic reasons,
we go with 'ㅅ'
It's like a rule, so please remember
HOT --> 핫
PODCAST --> 팟캐스트