Rules as Written it's odd that kobold tunnels can accommodate humans perfectly and without squeezing, as they occupy the same sized "space". And it's odd that humans can't go sideways down a 2-foot-wide corridor, or even fit through most doors in their house (which are about 2 1/2-feet-wide) without having their speed reduced.
Rules in Play this doesn't matter for a second. As each and every D&D game is run by an intelligent, thinking human being that can look at the description of the elf bard and say "yeah, you can totally squish through there" while also looking at the half-orc barbarian and saying "eff no, even greased and naked I need a Dexterity check."
It's not really a relevant or important concern.