From the site Why is the RSA Factoring Challenge no longer active?
Various cryptographic challenges — including the RSA Factoring Challenge — served in the early days of commercial cryptography to measure the state of progress in practical cryptanalysis and reward researchers for the new knowledge they have brought to the community. Now that the industry has a considerably more advanced understanding of the cryptanalytic strength of common symmetric-key and public-key algorithms, these challenges are no longer active. The records, however, are presented here for reference by interested cryptographers.
I think they've realized that with cheap cpu's and modern OS's, these challenges are more at risk, and can be cracked more easily. They just don't want to pay the money