As mentioned in Webtatic-5 repository EOL schedule, the only remaining package not in the other Webtatic EL5 repository, PHP 5.3, support was to be made End of Life (EOL) on Webtatic when PHP.net EOL's PHP 5.4. PHP 5.4 support on php.net is ending today, and as so, the Webtatic-5 repository is becoming EOL too.
Not to be confused with the Webtatic EL5 repository, which will continue to be supported for several years still, the Webtatic-5 repository was the original first repository this site hosted.
It served packages in a format that was easy to install, but bad to pin (it has conflicting package names with RHEL/CentOS base packages), and so the Webtatic EL5 repository was created to change that for new packages.
Both Webtatic-5 and Webtatic EL5 host the mysql51 and mysql55 packages, and so with Webtatic-5 becoming EOL, it will be redirected to the Webtatic EL5 repository in order for these packages to continue to receive updates.