I seriously don't get it. Netherite armour doesn't give you any extra protection nor is the knockback reduction generally useful (especially if you're playing on singleplayer) and the tools, while they do get a speed bonus, aren't that impressive either since you're probably also sporting Efficiency V tools and a Haste II beacon by the time you acquire netherite, meaning your diamond tools will already have instamine. The only upgrade that really comes into play is the durability extension but it's easier to repair diamond gear than netherite gear (since netherite is harder to acquire) it seems like endlessly repairing your diamond gear would be more beneficial in the long run.
This all, to me, makes netherite gear kind of redundant and, frankly, useless. Yet people seem to be going crazy over it. It's like you haven't really won the game if you haven't got it, which I really don't get. What is it that I'm missing? What makes netherite so good?
Repairing? You do use Mending, don't you? I sure wouldn't ever think of not using it as it would be incredibly disruptive to my playstyle to have to constantly make new gear (I mine an average of 4,700 blocks every single day - a diamond pickaxe won't last long at that rate, considering you can only work on an item 6 times before it must be replaced, including making it in the first place).
That said, armor does have more toughness, which means it is more effective against stronger attacks - most armor loses 1 armor point for every 2 points of damage; full iron loses half of its protection from a 15 damage attack, while full diamond requires 40 damage to lose half its protection and full netherite requires 50 (although such a damage source kills you either way; on Normal a creeper deals up to 49 damage, but the extra protection does help. It'd be much better if it wasn't affected by armor penetration at all, behaving like armor before 1.9, where you can survive 100 damage regardless of whether it is one strong attack (e.g. charged creeper) or many weak attacks).
Also you can kill zombies in two hits with a Sharpness V netherite sword, which deals 11 damage per hit (zombies have innate armor so even at maximum penetration, which requires 3.2 damage or more, they require 20.3 damage to die, just 0.3 too much for a diamond sword); the extra damage also enables you to attack slightly faster than the cooldown allows for fully charged attacks and still kill most mobs in two hits.
Also, beacons have a major flaw which explains why I've never bothered with them - you must remain within only 50 blocks of them, which is nothing when I've explored up to 300x300 blocks in a single play session while caving, even further when including sessions where I explored widely separated areas; most of the blocks I mine are also ores, which can't be instantly mined (that said, there may be no difference between diamond and netherite due to the way the game calculates mining times; it is rounded up to whole ticks or 0.05 seconds and an additional delay is added unless the block can be instantly mined. In particular, wood and gold can mine stone just as quickly when they have Efficiency V):
This is an animated rendering of what I explored underground over a 30 day period; the area shown is over 1,000 blocks across with the separate bit to the upper-left a stronghold (previously found with eyes of ender to get to the End, later rediscovered while caving); over this period I also mined more than 141,000 blocks:
[...] What is it that I'm missing? What makes netherite so good?
Even though the difference may be small, a Netherite armour/tool is just objectively better than its Diamond counterpart (unless you care about repairing it in an anvil, which the Mending enchantment obsoletes).
But I think that a lot of the hype is less about "Mojang added something that's a little better than Diamond", and more about "Mojang actually added something that's a little better than Diamond after so many years, which proves that they might be willing to do that again in the future as well. What will be the next thing that they do this with?".