Reason 1 - Some html or web editors on the market allow users to create a web page and automatically inserts Lorem ipsum text as a place holder, the users leave this text in.
Reason 2 - Similar to reason 1, there is a word processing or dtp application on the market that allows the users to create websites and also contains default lorem ipsum filler text. (eg Aldus Pagemaker)
Reason 3 - Internet hosts provide default websites for their customers which contain Lorem Ipsum text.
Reason 4 - People use Lorem Ipsum text on their web sites and forget to delete the text or have their websites indexed by search engines before the blind text is removed.