I have no idea. Perhaps because they don't know how to make money with splogs
Is they need something new - just give it to them. There is no problem to do have an unique content on splogs.
Here are my stats for 2 average domains:
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splog (PR2) - updates every 2 hours
Month Unique visitors Number of visits Pages Hits Bandwidth
Apr 2008 46626 53712 122293 876760 8.90 GB
May 2008 42656 50351 176379 817876 9.05 GB
Jun 2008 45395 53194 166577 784759 9.50 GB
hand-written blog (PR2) - updates a few times a month
Month Unique visitors Number of visits Pages Hits Bandwidth
Apr 2008 10742 12826 57264 432092 14.77 GB
May 2008 11324 14084 72861 460373 14.18 GB
Jun 2008 10293 12793 59800 393658 11.14 GB