It's bad power - transients apparently kill LEDs quickly.

Me - I have the exact same bulbs in my off grid property, and in my on-grid property. On grid, it's about 18 months MTBF. Off grid - it's been seven years and I haven't had to replace a single bulb yet. On-grid our power is anywhere between 205 and 235v, often has spikes up to 260+, and has like 99% uptime. Off grid, it's 230v, day in, day out. Grid power is terrible in most places.