Those saying it's old music are technically right, but they're missing the point. Linkin Park tapped into something genuine about teenage and early adult angst that simply doesn't age, no matter when the album came out. "In the End" doesn't sound dated because the song is about futility and acceptance, not fleeting trends. The synth and distorted guitar are just the packaging - the emotional content is what takes you back to high school every time.
What's interesting is that the band never got obsessed with sounding "modern" or chasing whatever trends were happening at the moment. Other nu-metal groups from the 2000s wanted to be heavier, faster, more extreme. Linkin Park just made structured songs with obvious melodic hooks combined with lyrical vulnerability. That's way more resistant to the passage of time than trying to be the coolest band of the decade.
One thing you can do if you want to better understand why it still hits is listen to their more recent albums without bias. A lot of people get stuck on "Hybrid Theory" and "Meteora" and assume everything else is worse, but if you analyze them without comparing, you'll see the sound evolves while keeping that emotional structure that grabs you. That way you realize it's not just nostalgia - they actually know how to build a song that works.