You just wrote, "gives me anything I'd want from Ranger..." That means things that are important to you, not someone else, so that's it in a nutshell right there. If you don't care specifically about Hunter's Mark, Natural Explorer, Nature's Veil and the other class-specific features, then you're right. Easy to duplicate a Ranger.
Hunter's Mark is basically a variant of Hex. Nature's Veil is a small number of 1 round invisibility as a bonus action uses per day gained at 14th level. Natural Explorer is unreliable as you might not always be in the correct terrain type to use it. It's replacement, Deft Explorer is two languages and an Expertise, then later a speed boost (with other movement speeds)- some of these can be replicated or superseded by other class abilities if you want them. Primeval Awareness is a Commune with Nature with a smaller area, but likely usable more times each day.
It comes down to whether or not this specific package of abilities is what you want, I guess. Deft Explorer is equivalent to the Scout Rogue's Survivalist and Roving is the exact same ability as the Scout Rogue's Superior Mobility. There's very little that's truly unique about the Ranger's abilities is what I'm getting at. So yeah, if you want everything the Ranger provides, then the Ranger is the class for you, but a lot of what I hear from people is they don't want everything the Ranger provides- no spells, no Hunter's Mark the class, etc. etc., and would rather have other things.
And it turns out that the combination of "what you'd want from Ranger and dispensing with what you don't want" is perfectly available with other classes and subclasses. Again, it's a perfect storm of a lack of justifiable niche protection + the multiclassing rules that makes this so. I'm not telling anyone they have to like it. It's just that, if I sit down to make a character, even one that fist the Ranger archetype, I don't have to be an actual Ranger to get the results I want. And nothing about the Ranger strikes me as so unique and cool that I really want to play a Ranger- that's a personal preference, obviously, but it's been like that a lot over the years. I contemplated making a lot of Rangers, but never actually did (outside of that one time in 4e and a 13th Age one-shot which barely counts) because "Druid-flavored Paladin with less defense and unreliable class features" wasn't for me. I know that description sounds reductive, and it is, but that's how I personally felt about it.
Now subclasses can elevate a class in 5e. I was initially interested in having an animal companion, until I saw how tepid the initial version of the subclass was and I never went back. I actually wanted to play a Melee Hunter, when I realized they'd given the Ranger some abilities that used to be in the Fighter's wheelhouse, but ultimately felt that it felt defensively a little short, with no really obvious way to patch that. Maybe I gave up too soon there, but it felt that I'd be better off being a Ranged Hunter, and my first 5e character was an archer Battlemaster/Rogue so I wanted to do something different. Plus, I'm going to admit I have never liked Hunter's Mark. It just felt so damn fiddly, cast a spell to give me a damage boost against one enemy which I then have to juggle around and worry about losing concentration on? The heck is this? If the class is built around it, why isn't it just a class feature like Sneak Attack? I don't care how good it is or isn't, it just sounds annoying to use!
