Example: Jakob Nielsen publishes research that shows "people on the web don't read." The sample content used to determine this? The list of tourist attractions in North Dakota.
Garbage in, garbage out.
Finally, the vast majority of text on the web around forms etc. is useless, poorly written, obtuse, abstruse. People have been indirectly trained to ignore it. It's not surprising that most users ignore that messages you took the effort to write.