I will say I’ve been quite a few street fights(not saying I’m the toughest just the truth) and I’ve never thought of this until last few years after seeing people get hit and die on the news falling on pavement. So I agree to find another surface to fight on but sometimes no choice but as you said they were on the beach and should have justripped it up there if they wanted to fight.
In an urban environment there is no choice.
Living in Houston most of my life i saw a lot of dudes hit pavement hard. When 90% of the City is paving, it's not like you can just drive a few blocks to the local park.

But when you are fighting someone, you are usually so fired up that logic goes out the window.
Nobody is going to fight on sand. Too hard to move your feet.