There are various reasons for this, primarily because the game was excessively successful, prompting the producers to make a U-turn.
1. Portal

Initially, Portal was released as part of The Orange Box bundle, but it became a phenomenon within the gaming community. Its humor, unique gameplay, and creative puzzles made Portal an unforgettable title, with GLaDOS becoming one of the iconic characters in the gaming industry.
The ending scene where the protagonist, Chell, defeats GLaDOS, the room collapses, and Chell wakes up outside Aperture Science's Enrichment Center is considered a satisfactory conclusion, although fans still debate it. Additionally, Valve hinted that GLaDOS was still alive through the end credits song 'Still Alive.'
About two and a half years later, in 2010, Valve updated Portal with an extended ending, showing Chell being dragged away by a robot, and Portal 2 was announced shortly after. In summary, playing the first installment wasn't necessary to enjoy the second. Furthermore, Portal 2 received critical acclaim and praise from both professionals and fans.
But about two and a half years later, in 2010, Valve updated Portal with an extended ending, revealing Chell being dragged away by a robot, and Portal 2 was announced a few days later. In summary, it wasn't necessary to play the first installment to enjoy the second. Additionally, Portal 2 was an outstanding game and received much praise from both professionals and fans.
2. Tomb Raider: The Last Revelation

During development, Tomb Raider: The Last Revelation was promoted as the final installment due to the developers' lack of intention to continue. Consequently, The Last Revelation was depicted as dark and with a less-than-satisfactory conclusion. This shift garnered high praise and acclaim for the game.
As a result, developer Eidos decided to release Tomb Raider Chronicles the following year. Despite being a prequel, Chronicles ended with Lara still alive, paving the way for The Angel of Darkness set after The Last Revelation, reintroducing Lara to gamers.
Ironically, both subsequent releases were heavily criticized and performed poorly in sales. Consequently, Tomb Raider was handed over to Crystal Dynamics, while the production studio Core Design had to shut down.
3. Max Payne 2

Max Payne was among the most beloved shooting games in the early 2000s, and its sequel, Max Payne 2, stood out as one of the finest sequels ever produced. The climax featured Max Payne unleashing gunfire to eliminate all who dared to cross him, with his lover Mona Sax enduring sacrifice amid the gunfire.
In the conclusion of Max Payne 2, players witnessed a painful yet complete ending for him—a testament to his acceptance, confrontation of the past, and overcoming of that pain. Even the game's creator, Sam Lake, deemed it the most complete conclusion.
However, Rockstar Games still decided to revive this series with a third installment, where Max Payne becomes a washed-up alcoholic living in Sao Paulo, Brazil. No longer bearing the noir essence, Max Payne 3 is a completely different game altogether. However, it bears no resemblance to its predecessors.
