I think this goes back to the early days of web development. Before we could add fonts with CSS @include and had to write progressive websites (yay 800x600), everyone who wished to use custom or platform specific fonts had to generate images with that text using a php script or some such. Since government IT is chronically underfunded (IMO) and the web hit critical mass late 90s/early 2000s - long before best practices or new technologies could be widely disseminated - most of them are stuck in that time period because that's when they were first forced to support the web.