Two possibilities:
1. PEBKAC
2. They died because they are hard drives, not because they are Seagate.
Personal anecdotes are worthless. I have hard drives made by Seagate, Maxtor, Hitachi, Western Digital and others. Recently I had a WD die on me after four years, but that certainly won't stop me from buying another.
Talk to someone who manages large RAID clusters. Hard drives in those arrays are hot swappable because they have drives die literally every week. It doesn't matter who makes them. They just die because hard drives suck.
The only time I've had a hard drive die that was actually a bad product was a 40 GB IBM DeskStar, which are legendary for abrubt failure.
Bassoon, n. A brazen instrument into which a fool blows out his brains.