I think the main reason would be the obviously mis-perception of the value of your company. I do believe people still look at crowdfunding sites like kickstarter and indiegogo as hobby or fun-type of investing as opposed to serious investment. Another reason would be the amount of investment dollars you are looking for and the unknown aspect of whether you could hit that target or not. With some crowdfunding platforms it's all or none in terms of hitting the investment goal amount and being able to actually use the investment, which poses a concern that if you ask for $1mm and you get $990k the entire effort could be lost.
All that being said, crowdfunding is an extremely viable resource and should be considered by everyone - at least for their early stages.