Why default pool "Reselect Tries" to 0? Any downside to higher values? Wouldn't that prevent client failures?

My main concern would be for persistence, since re-selecting another pool member before the F5 has marked the original selected pool member down may cause more problems than it solves as re-selecting may break the persistence paradigm. There are many reasons to have a failed TCP connection that might not be indicative of a node truely being down.