Hiya!
My guess? "They look cool!". After that, it's purely the munchkin/min/max/PC-Build-Is-All-Important type people who only see the mechanical effects and could care less about anything else. Then there's the majority of people who think somewhere in between.
But, from MY EXPERIENCE, mostly the first "it looks cool" side of the equasion. It's never been a 'problem', not for long anyway.
What I mean is that my campaign is quite "old school humancentric". Humans rule the roost, so to speak. They are THE most adaptable and variable and most mutable of ALL the races
in existence. It's their 'schtick', so to say. So, if a party of two Tieflings, one Half-Orc, one Dragonborn, and a Gnome walk into town...well...they are going to get the cold shoulder, mostly. The Gnome will be the one who gets addressed 9/10 times, often to the point of rudeness.
For example, the group is at a leatherworkers stall in the marketplace. The Dragonborn is looking at an unusually decorated large belt pouch with belt and asks "Is this oiled? You know, water resistant?", the vendor may give the Dragonborn a slightly quizzical look, then turn to the Gnome and say "Uh, yes, but only lightly. Does he want it?".
That kind of "human-centric", with the 'typical friends of humanity' being generally accepted as equals (re: elves, dwarves, halflings, and gnomes; half-elves and half-orcs, a bit less so, but still ok). The races that look "more something-else" than human are treated as just that...something else.
^_^
Paul L. Ming