I'm not sure why some places require 5x rent in income it is wildly excessive. My personal theory (based on hunches only I have found no evidence for this) is they want to only attract tenants who are less likely to leave after a year or two of 10% rent increases. They may also be trying to push gentrification by making sure only well off people enter a neighborhood, fuelling the need for more "luxury" apartments to be built and perpetuating their industry. Idk, they're pretty tight lipped about the reasoning if someone has more insight into their motives I would love to know