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I think the difference is that we ride a lot on clay surfaces (the second picture). When those get wet, you get al sorts of 'unique' problems. For starters it is almost impossible for tires to get any grip on it. As such running or walking is often much faster compared to staying on the bike. Another issue is that it clogs your drivetrain unlike anything else, resulting on tons of dropped chains (reminds me I need to get a chain guide before the rains set in).
and there are a lot of people walking in that 2nd, ive seen worse mud in epping forest on a summer badgers ride