[angersock]

Long story short:

JWZ created XScreensaver back in the day, using raw Xlib.

He did this because he did not trust the security of larger toolkits/programs--a screen locker must be so simple that it can't go wrong, and none of the larger libraries is auditable/verifiable in that respect. If it crashes, somebody gets access to your desktop.

Every five years or so, some group in the *nix community decides that they know better than Grandpa Zawinski, and they reinvent XScreensaver--however, they usually do so poorly, and insecurely.