Why is there a draw in professional chess? I'm not a serious chess player, but I heard that about 80% of professional chess games end as a draw.

In other similar abstract strategy games, such as Shogi and Janggi, when it is impossible to checkmate, they evaluate pieces value and determine the winner (in a professional game).

Why does chess not adopt this way?
First of all let's put the numbers correct. 

The 80% draw ratio is for correspondence chess, not something that the average person would associate with "chess".

In regular top level chess, the draw ratio is around 50%.



In either case, most games are not played out until a postions when it is impossible to checkmate, but rather most draws are agreed draws, i.e. draws in a position that could in principle be won by either player through checkmate.



If I understand your proposal correctly, you want to get rid of draws completely by evaluating dead positions (that cannot be won by either player, not even if cooperating) according to the piece value.

I see several difficulties/issues with this approach:


You'd have to decide what to do with perpetual check, stalemate and the 50 moves rule.
What do you do with positions that are equal/drawish with equal material but that are not dead draws (i.e.  either player can still checkmate)? Forcing players to continue until dead draws could lead to very long (and boring) games, similar to what we see with some games under Sofia rules.
Positions where it is impossible to checkmate are pretty rare. Basically only King vs King or King and one minor piece vs King (and a few exceptional/constructed cases). In the large majority of positions checkmate is possible if players cooperate. So the proposed change would not alter much.
If players in the dead draw position would have equal material it would still be a draw.