Why brands do this
Modern luxury watch brands have learned that scarcity drives prestige and protects pricing power. If everyone could walk in and buy a Royal Oak, the Royal Oak would lose its scarcity-status premium and resale value would collapse. Brands like Rolex (~1M watches/year), AP (~50k), Patek (~62k) deliberately produce volumes that cannot satisfy demand at retail price. The waitlist becomes part of the product.
Which watches are hardest
Patek Philippe Nautilus 5711/1A-014: the most-recently-discontinued steel Nautilus, last available 2021. Grey market 3-5x retail. Audemars Piguet Royal Oak 'Jumbo' 16202: thin-cased Genta-spec Royal Oak; AD-only after 5+ year purchase history. Rolex Daytona 116500LN ceramic-bezel: 5+ year AD wait; grey market 2x retail. Patek Aquanaut 5167A: 4+ year wait, 2-3x grey premium. These are the modern poster children for supply-constrained luxury.
What you can do
Build an AD relationship: buy 3-5 less-allocated pieces (entry references, women's watches, smaller-diameter pieces) over 1-3 years to establish purchase history. The AD eventually offers you the references you actually want. Buy grey market: 1.3-2.5x retail but immediate. Pre-owned: usually similar to grey market for current production, but more depth on discontinued references. Wait it out: brand allocations cycle; references get reallocated, new references launch. The 5711 is gone but the modern 5811 (white gold) replaces it.
The brand calculus
From the brand's perspective, the supply-constraint strategy works because resale value protects current owners (so the brand stays desirable), retail prices stay high (no discounting pressure), and brand mystique compounds (the watch is exclusive partly because it's hard to get). The cost is that some legitimate buyers walk away to alternatives (Grand Seiko, Lange, F.P. Journe), but the brands have decided that loss is worth the strategy. See: vintage market boom.