Why are Wilt Chamberlain forever stamps are selling way more than 47 cents per stamp? Is it already a collectible stamp? USPS is out too.?

The Chamberlain stamps were issued in 2014. That's over two years ago. Yes, the Wilt stamps were issued to be a collectible. USPS makes millions every year by selling stamps that are never used. The Postal Service typically doesn't stock commemoratives for more than 12 months, except maybe at their Philatelic Sales Division. The prices in excess of face value are people selling at a profit. That's good business.

I share your admiration for the design of the stamps issued in his honor.

Nobody collects stamps anymore

Forever stamps are stamps that retain the value of a stamp for that year...