Why Malaysia 1st RM5 Copper commemorative coin price drop badly after 2 year ?

Описание: Few years back this coin sold around RM4000 to RM5000 in Bank Negara Auction but today it is possible to buy around RM1,500. Why did it drop so much after 2 years?
(Do forgive me on the ending , i always find it hard to do my ending.)
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