They aren't all in small quantities. Most days I can recall seeing 50k - 100k or even 150k - 500k blocks being bought as well. Also some of them could be broken out based on the limit price desired and if they traded without selecting "all or none" on the quantity desired. For smaller blocks I would assume that some people don't have a lot of money to throw around or have diversified investment portfolios. Different investment strategies for different folks.
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