Because this was your problem doesn't mean that it is common. If you had been checking your fluid level (look at it when you check the oil), you would have caught this. Also, you could have see the leakage, had you inspected the calipers, which is harder to do.

The seals in the calipers deform under use, and don't slide along a bore like the master cylinder seals or seals in the slave cylinders of drum brakes, which we don't have. The pistons proceed through the seals very slowly, and are very unlikely to fail before the piston sticks for other reasons.

Don't fall into the trap of thinking that your bizarre problem is what affects everyone else.