These sets are at the end of life. Means every product is designed to last for some time and then get out of stock. If this moment is reached, the set value will increase significantly. Therefore EOL-Sets are very popular. But please be aware that some sets are listed as “EOL” just because it gets out of stock from LEGO for some moment until they restock them again. So even if it is listed here, it is not 100% reliable.