Why is losing on time when opponent has insufficient mating material not considered as a draw?

@h2b2 of course lichess has endgame tablebases. Just set up a position on the analysis board and press the book icon on the lower side of the notation. See e.g. in post #2 here.

I see mate in 4.

1. Kg2 Kg4 2. Kh1 Kxg3 3. Bd4 Bf5 4. Bg1 Be4#