Why do these other designs not fit?

I believe the relevant part of the log is this bit:

nfo (170239): Router is attempting to preserve 23.61 percent of routes from an earlier compilation, a user specified Routing Constraints File, or internal routing requirements.
Info (170236): Routing optimizations have been running for 1 hour(s)
    Info (170242): 0 out of 364996 signals have been routed.
    Info (170238): 804177 interconnect resources are used by multiple signals.
Info (170195): Router estimated average interconnect usage is 60% of the available device resources
    Info (170196): Router estimated peak interconnect usage is 186% of the available device resources in the region that extends from location X165_Y189 to location X176_Y200
Info (188005): Design requires adding a large amount of routing delay for some signals to meet hold time requirements, and there is an excessive demand for the available routing resources. The Fitter is reducing the routing delays of some signals to help the routing algorithm converge, but doing so may cause hold time failures. For more information, refer to the "Estimated Delay Added for Hold Timing" section in the Fitter report.
Warning (16684): The router is trying to resolve an exceedingly large amount of congestion. At the moment, it predicts long routing run time and/or significant setup or hold timing failures. Congestion details can be found in the Chip Planner.
Warning (16618): Fitter routing phase terminated due to routing congestion. Congestion details can be found in Chip Planner.
Critical Warning (188026): The Fitter failed to successfully route the design.  You may be able get this design to route by making design modifications, changing the fitter seed or by enabling the Fitter Aggressive Routability Optimizations logic option.
    Info (188027): The highest placement effort tried by the fitter during this compile was: 1.54
Error (170143): Final fitting attempt was unsuccessful