Nice to be back.
Videogame endings are terrible. There are exceptions, but I'd hardly call them numerous enough to uphold a statement to the contrary. Here are some of the things games often provide:

A. A final boss difficulty spike,
B. An unsatisfying plot resolution,
C. No plot resolution (the cliff hanger),
D. An underwhelming final boss (‘is that it?’).

One – or a combination – of these occurs for several reasons. The most apparent is that there simply is not the talent available to pen a satisfactory conclusion. It takes skill to orchestrate a well-paced storyline: riveting, winding, unnoticeably and rhythmically rousing to a fitting endgame designed to leave the player watching the credits with fulfilment. Games are, after all, interactive experiences. Time and money is invested in the pursuit of something enjoyable to play, making the mechanics solid, the levels intuitive to navigate, the physics pleasingly malleable. Script-writing is pretty far down the list of priorities.

This is the first glaring oversight the games industry is guilty of:

GLARING OVERSIGHT #1: GOOD STORYTELLING MAKES MORE ENJOYABLE GAMEPLAY.