Once upon a time, it was intended that attaining a high score or reaching a particular wave or level was the goal, not "beating" or completing a game. Keep in mind that replay value goes up if you have your own (or someone else's) previous high score to beat.
Note, too, that in some cases, a harder level meant decreasing a countdown timer start value so that your character or enemies moved faster. Eventually, the game is going so fast that you simply cannot react quickly enough.
To be honest, growing up with an Atari 2600, I had no concept of "beating" a game with no intent to replay (even Star Raiders gave you a rating you could beat next time you played) until the NES and games such as the Legend of Zelda, in which there was no score or time to beat.
In this way, the arcade and computer games I started with are games of skill, much like pinball.