It’s not so much that they are fragile, as they’re a part that gets a lot of very heavy duty use and they’re expensive to make invulnerable. Ain’t no residential customer going to pay for a 100mfd 240v tantalum cap (how big would it be even?).

Think of them like a car starter motor or transmission (for old ICE vehicles).

Assuming we’re talking motor start capacitors anyway. For most of them, every time the compressor starts they see a dead short at 240v for a couple milliseconds, typically in the 10,000+ amps range.

And most people use their AC the most when it’s hot and nasty out. Which doesn’t help.