I assume those floor drains lacked a functional p-trap because I've read with covid that disease would spread through drains without a proper p-trap, but otherwise the p-trap prevents drains like toilets and sinks from stinking and allowing contaminated air through.
P-traps can dry out though, but they stink if they do. Maybe that's what happened there?
Edit: yes, that's the theory - floor drains with dry u-bends allowed the poop air out.