Why?

Most likely not concentrating on the mechanics of a foot launch. Getting the nose down, holding the downtubes back. Spending a lot of time aerotowing and less time foot launching, although I've done a lot of that lately, some times as poorly as the example shown in the video (which is why I had two other poor launches with less good outcomes here in Manilla).

What isn't shown in the video?

There are very light breezes coming up the cliff launch that is the west launch at Mt. Borah. It is topped by a flat slope launch which isn't in the breeze at all. I have declined the launch just prior to this, getting out of the way for another pilot, so I am unsure of my ability to have a safe launch. I had just crashed on the north launch about forty five minutes previous to this.

You will note that I am a fair distance back from the lip of the flat slope. I am back there in an attempt (failed) to get enough air speed to get the glider to float off the hill when I reach the edge of the green carpet. That would have required keeping the nose down.

Here is the launch sequence slowed way way down: http://ozreport.com/badlaunch.php.