I don't actually think it's about this at all. Limited games play themselves more than any other format. Sure, there's variability in the form of ever changing decks, but I don't think this actually creates depth of gameplay. Depth of deckbuilding, sure.
I think if anything depth increases with known quantities that can be played around / interacted with, e.g. "I know my opponent plays Stifle and Wasteland, how does that affect my land sequencing? What risks am I willing to take?" or "My opponent has left X mana open, what is he representing?" "Opponent played Hallowed Fountain untapped T1 on the draw and passed the turn. Is he holding Spell Snare? Can I afford to play around it? What are the costs of taking another line?"
The fact that decks are shuffled already mixes things up. The best Magic matchups have loads of replayability. A skill-intensive matchup where you could jam matches for hours and still be having fun. You can't do that in a lot of Magic, and I certainly wouldn't want to do that with most limited decks.
I can play Protoss vs. Zerg for days on end. I can do the same with Marth vs. Falco, Black versus White in chess, Red versus Blue on a fixed map in Halo.
Imagine Magic's churn of new cards stopped. How long would you want to play Standard with a fixed card pool? I think picking the best deck for a format is super skill intensive (be it draft or constructed), but often piloting that correctly doesn't have a lot of depth to it.
How often do you watch a Magic game and walk away feeling amazed at the play? Did the player inspire you, or just not make any mistakes? How often do you watch a player win a game and think "there's no way I could have won that"? I get that feeling a LOT when watching masters play Legacy. Less in Modern, and almost never in Standard.
