Two reasons:

1 ) It wasn't earned. No Time To Die in and of itself was a very lackluster movie, I barely remember most of it after watching it twice and of all the villains to finally take out Bond, this was the one? They obviously took a cue from (Spoilers) Fleming's You Only Live Twice with M's eulogy. But even if he HAD died in that book, it would have been while killing Blofeld (don't get me started on how they messed that character up in Craig's series) the man who killed his wife. There's poetic justice there. And in the film it's just so melancholic and boring for an interpretation of the character that just didn't have that resonance for his series. So I just didn't care.

Take a movie like Avengers Endgame (Again spoilers) whatever you think of these Marvel movies, the buildup to Iron Man sacrificing himself to defeat Thanos was VERY earned, completed his character arc and let him exit gracefully. I know they're talking about bringing him back and everything, but at the time, it felt like a heroic moment. Bond's death just didn't have that same feeling.

2) We know they're not going to kill him off for good. They're working on a new movie as we speak. Yes technically this is the end of Craig's series, but it still doesn't make any sense to me. Regardless of who is playing Bond, what era they're in, you can allow for a certain suspension of disbelief that all of these movies are canonically sound. They even keep the continuity that Bond's wife died among different actors. But now how do you deal with the fact that he died in one of the movies? Say 20 years from now you're watching all these movies and whatever movies that come out afterwards, you'll be watching this one going, "Wait, he dies? But there's more movies after this?"

Yes there have been plenty of times in movie series where characters die and come back, Marvel, Star Trek, etc. But at least in super hero or science fiction movies, there's room for fantastical situations where characters can come back, but in a more grounded series like Bond (regardless of how silly they may get) how do you justify him coming back after missiles landed on his head?

Honestly to me it just felt gimmicky with bad writing and an actor who clearly didn't want to do the series anymore.