1, Because it has a very good chance of unseating the $160 bid, which would get this set moving again.
2, Because most sets go for lower than the bid that crosses the line - so if you only want to pay $40 or $30, getting it past the line at $50 is your best shot.
3, Because Logos possibly 'helps' some of these sets, and so we need to get the $50 price up before the $160 is helped.
4, Because it's Revelation!!!
5. Because if we wait much longer, we won't need to read about it all in books.
http://www.logos.com/product/8522/classic-commentaries-and-studies-on-revelation