Not sure about other boats and the flow coat on those boats. But mine, the flow coat (finish) can get quite slippery when wet, which it is wet most often.
And I'd have to concede that I probably don't always wear the most appropriate footwear, and really, how many of us always do, even guests, who may get caught out.
Given I have kids too (ruddy rascals) who have fished on the boat since they were young.
So for me, it was definitely a safety concern but equally, peace of mind. Especially when overexuberant focus is on netting a fish, or lunging for a buckled rod and focus taken away from a possible slippery floor.
Cheers, Bugatti, who thinks fish should be the only slippery buggas on my boat , , , , well, not including me, that is