Here's a little challenge for you: very quickly - no Googling - try and think of a video game that doesn't have a single boss fight.
Aside from the obvious titles (sports games, walking simulators), it's genuinely quite hard to think of an example off the top of your head. Boss battles are one of the longest-standing tropes in the video game realm and have been around for decades at this point, so it's no surprise that they're bloody everywhere.
And so, whenever you're playing through a story and you bump into a bad guy, there's no reason to assume that you won't get the chance to kick their ass at some point down the line, but that's not always the case.
Especially in contemporary games, a lot of "bosses" are dealt with via cutscene, with limited or nonexistent input by the player. This isn't always a bad thing - it's still possible to give a villain a memorable send-off without any interactivity involved - but it can sometimes sting a little when you're denied the satisfaction of beating up a boss with your own two thumbs on the sticks.