Surely you clean and lube your chain more often than once a month or 1500-2000 km? I usually lube mine at least once every 100-200 miles and clean them after 200-300. Even at that, I wouldn't expect much more than 8000-10,000 km out of a middle chainring. I generally replace chains and most-used cogs about every 3000 miles. I commute 22+ miles round trip every day, often enough in rain/wet to get the drive train gritty on a regular basis.
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