Why is this game a draw (insufficient material)?

I just finished playing a game in which I clearly won on time, yet as my opponent's time expired the game was "drawn due to insufficient material."

https://www.chess.com/live/game/3735168330

What kind of rubbish is this?

Your lone king could never have won.

so even if u win on time u still need to be in a winnable position otherwise its a draw? thats kind of messed up

so even if u win on time u still need to be in a winnable position otherwise its a draw? thats kind of messed up

Correct.Insufficient material=draw. Same rules as over the board chess. You should be happy with a draw, since it was mate in a few moves. 

Chess.com follows USCF rules (almost).  In this case, it is a draw no matter what.

USCF - Lone K, K+B, K+N, or K+N+N and opponent has no pawns is considered "insufficient mating material" and you must demonstrate a forced mate to win, otherwise it is a draw.  All other material combinations for the side with time wins.

FIDE - A LEGAL set of moves that leads to mate, no matter how dumb, must be demonstrated to win.  So:

A) W: Ka8, Bb7

     B: Kh8, Ph7, Qb1

This is a win for White if Black runs out of time.  Black advances the pawn to h2, king to h1 as White gets out of the way with Bc8 and toggles the bishop.  Once the king is in the corner, then Bh3.  Black toggles queen allowing white king to f1, and then Bg2 mate.  This would be a draw in USCF or chess.com.

B) W: Ra8, Qf7, Ra6, Pf4, Kh1

     B: Rg2, Bf3, Ra2, Be3, Kh7

Black runs out of time.  While a win at chess.com or USCF, draw in FIDE because the only legal move for Black is to mate white, so no legal series of moves leads to the black king mated, so it is a draw.

Timeout+insufficient material is a rule that ensures that a person won't lose on time when they have a completely winning position. The side winning on time must also have a theoretical chance of actually mating the opponent, no matter how slim (K+pawn against K+Q+R is still possible to win by queening the pawn and mating your opponent, even if the chances are extremely low).

In your game, black clearly outplayed you and it would be rather unfair if black lost on time in such a winning position. Therefor, the rule is implemented

This rule has been in place for longer than I lived, at least.

All you need is one surviving pawn and you will be able to obtain a win if your opponent flags.

I don't understand how someone who has been a member here for 10 years could be asking the question.

It seems very hard to believe that it never came up previously.

Perhaps...

He/she never logged in for years? (Have not checked his/her game statistics though)

Uh, no.

He has more than 10,000 games played and has been active all along.

It was a draw because you need to have sufficient mating material to win on time.  The exception to this rule is two knights, because you could still checkmate the opponent although it cannot be forced.