Probably just volume of traffic rather than the size of the assets. Not everyone's personal site is hosted on auto-scaling could services et al. So often you'll see stuff get "hugged to death" (as it's affectionately known) just due to the site's own popularity.
It's 5,000 words and 2,000 lines of javascript, plus a few fair-size images, which may explain the long TTFB. But most of the delay is not bandwidth limits but PHP and SQL. The site runs on a creaky WordPress implementation. Someday I'll fix that, if I live so long.
However the demonstrations are great, and some of the programs are inherently computationally expensive, so its sort of expected.