When an artist is the first to inspire a movement, history tends to look back on them differently. There’s a related trope that covers this phenomenon - “Seinfeld is Unfunny.” From that page:

There are certain works that you can safely assume most people have enjoyed. These shows were considered fantastic when they were released. Now, however, these have a Hype Backlash curse on them. Whenever we watch them, we’ll cry, “That is so old” or “That is so overdone”.

The sad irony? It wasn’t old or overdone when they did it, because they were the first ones to do it. But the things it created were so brilliant and popular, they became woven into the fabric of that work’s niche. They ended up being taken for granted, copied, and endlessly repeated. Although they often began by saying something new, they in turn became the new status quo.

Nirvana is one of the artists mentioned under the “Music” examples on that same page. The point is, they were groundbreaking when they came out, but they changed the music scene so much and have inspired so many similar artists that their original work has become overshadowed by the successors they helped create.

Your experience is common and it’s okay not to enjoy their music, but the key to remember is that without Nirvana helping to pave the way, other grunge bands may not have risen to the popular level they reached.