It’s about cleaning. Kitchens are messy places – spills happen often, and if they’re not cleaned up quickly, they create an unsanitary condition, they smell, they can create a worse slipping hazard, etc. And a hard, smooth surface is easy to clean – you can quickly run a mop along for spot cleaning, and easily do more thorough cleaning when it’s time to close up. The consequence is that it’s a bit more slippery for people.
It’s much easier to require employees to wear non-slip shoes and have an easy-to-clean kitchen, than to have a less slippery kitchen that’s difficult to clean. The pros outweigh the cons.
It makes the floor much easier to clean, and quick/easy cleaning is a huge priority in kitchens. Smooth, sealed tiles can be mopped up very quickly and don’t have nooks and crannies for food to get stuck in and rot – the texture that makes something less slippery does so by creating those nooks and crannies. Since stuff gets spilled all the time in kitchens, every surface is designed to be easy to quickly clean.
It does make it easier to slip, yes, but as you pointed out that can be easily fixed with the correct footwear, which is pretty much mandatory in every restaurant and kitchen for this reason.
Great answers about being easier to clean but just one other note, if you are working in fast food, you are also working in an environment where there is grease everywhere. The grill will be cooking the patties which will inevitable have aerosolized grease end up on the floor. The person cooking the burgers will inevitably end up stepping on some of this grease on the floor and track it to where they put the cooked burgers. Then the prep person will walk through that while they are making the burgers and track it all over. Then the expo will walk through that when they are grabbing the food and track it all over. Same thing is happening at the fry station. So how you have grease from the grill and the fry station all over the floor of the kitchen, on a hard impenetrable surface made to be easy to clean, which means the floor is going to be slippery.
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