Peter Jackson had the luxury of telling a story that was already perfectly structured in the books, with unlimited budget, generous shooting time, and a clear vision without interference from studios obsessed with franchises. That's pretty much impossible now. Studios want trilogies that become 10-movie franchises, they want shared universes, they want to make decisions based on what works on social media. Most fantasy directors today simply don't have those working conditions.
That said, it's not just nostalgia. There's something real about LOTR being shot like it was a cinema film, not like content. Jackson spent years in New Zealand building the world, creating effects that age well because they're made with physical models and obsessive care. Current fantasy films have huge budgets but they spend them on different things - sometimes promotion, sometimes trying to cram in too many subplots. Pure digital effects can also feel flatter, less tangible.
The other part is that LOTR set the bar so high that nothing can surprise you the same way. You've seen the Battle of Helm's Deep, you've seen Moria, you've seen Smaug. Any other fantasy film is going to look smaller just because you know that scale. But yeah, I think if studios let someone make a fantasy epic without pressuring them to make it part of some bigger universe, something memorable could come out again. It's just that happens less and less these days.