Why do most modern video or computer games feature scrawny heroines and characters that look out of place in the game world they are in

because a memorable character, no matter how strange or out-of-place, will make people feel that a game is more involving and will make it a better RPG (Role-Playing Game) and it will sell more.
For example, some people buy art just because it was done by a famous artist, just like some people will buy a video game just because it stars Mario.

The only reason why people make games with such characters is so that it makes games easier to sell and more valuable to the buyer.