stg83: The reason for the slow start might be that there are two games instead of just one like it was in all previous insomia promos. Once you give people a choice they don't feel as compelled to buy just to see the next one probably.
That could be too. Plus it's a Monday, kind of an odd day to start the sale.
I think it's a combination of factors, including how long it takes the news to get around. Also, GOG probably should have started with two high-demand games, in order to jolt the news into spreading faster. Hopefully we'll see things pick up soon.
It will be interesting to see which category moves more quickly.