Research papers have no deadlines as to when they should be submitted to journals and can be sent to the journal editor at any time. Unlike teaching or other meeting-driven schedules where you must show up at a specified time, journal articles must be initiated by the author of the paper. Since most people are not self-starting or cannot initiate things on their own, publishing is very hard for most researchers. People are just too lazy to put forth the effort or cannot afford the time to devote to a writing project. Some scientists are too critical of their own work.
Some people are actually too picky and critical of their own work.
I have known several scientists that expected their research paper to be perfect before submitting it to a journal. While this is an admirable goal, the consequence of this high expectation is that the scientist cannot ever seem to get the paper ready to send to the journal for review. The data are not quite right or good enough, and the scientist always seems to need more data. People in this category conduct excellent research and normally have great data, but they still think someone may find a little problem with their work or be critical of the data, its analyses or interpretation. Some scientists cannot take criticism.