1. Corrosion 2. Electrolytic caps. 3. Vibration. 4. Flexing due to thermal cycling. 5. Electronic designs operating near their limits, resulting in increased failure rates.
It used to be everything in a hostile environment (hot/wet/corrosive) was potted (dipped in epoxy) and in an enclosure. Now they have bare boards. Electronically controlled motors and very limited protection circuitry for the ICs. Just not built to last. No commonality in circuit boards so parts are very expensive (possibly by design; they only need parts for warranty repairs, after that they don't care about cost/availability).
It used to be everything in a hostile environment (hot/wet/corrosive) was potted (dipped in epoxy) and in an enclosure. Now they have bare boards. Electronically controlled motors and very limited protection circuitry for the ICs. Just not built to last. No commonality in circuit boards so parts are very expensive (possibly by design; they only need parts for warranty repairs, after that they don't care about cost/availability).