It's a money spinner.
Manufacturers have every clue about how to make a reliable valvetrain system.
But a failing cambelt is heard of on most cars, so they can get away with it happening to their engines. When a cambelt fails, alfa make money. When a cam belt is replaced, alfa make money.
Why design a robust cambelt system when that probably earns them hundreds of extra pounds on each car.
Bulletproof Jap engines? I'm fed up of tripping over knackered japanese engines. Supra, GTO, EP3 CTR, 300ZX. Granted, they're fairly old, but they still have a reputation of being bullet proof when they're really not. They're reliable under normal 'trundling to the shops', but if you like to enjoy an engine they're crap.
Bottom end failures. They just can't cope with enthusiastic driving.
Give me a big yank V8 anyday. You can pound on them until your legs get tired and the engine, box, diff or suspension won't rattle, knock, smoke or snap...they just lap it up. You don't have cambelt or chain failures either....that's why they kept going bust.