We are about to commit a cardinal sin. Let's make a button:

<div class="button" onclick="someFunction()">Click Me</div>

Our button works if users click it with a mouse. But it is not keyboard accessible. Even if we add tabindex="0", which would make the <div> focusable, users who use a keyboard to navigate our site will not at all be able to click our button.

If we instead used a regular <button> element, it would be keyboard accessible. Try it out for yourself if you're on a keyboard:

<button onclick="clicked(this)">Good Button</button>
<div onclick="clicked(this)" tabindex="0">Bad Button</div>

false

function clicked(element) {
    element.innerHTML = "You clicked me!"
}

Browsers come bundled with a bunch of accessibility options. Whether that's something complicated like a screen reader or something simple like allowing the user to zoom in, browsers make our lives as developers a lot easier.

So why then do browsers not make our above button keyboard accessible? Because accessibility should not be the responsibility of the browser.

I get it. The default <button> styles suck and it's easier to style a <div>. But a <button> is the more accessible choice.

But I do think there is an argument to be made. Perhaps browsers should detect elements with an onclick event (or something similar) and automatically treat it as a button.

I can already think of a few problems...for example:

<div class="button" onclick="someFunction()" onKeyDown="someOtherFunction()">Click Me</div>

Now, this fake button behaves differently if you're using keyboard input:

<div onclick="someFunction(this)" onKeyDown="someOtherFunction(this)" tabindex="0">Click Me</div>

false

function someFunction(element) {
    element.innerHTML = "You clicked me!"
}
function someOtherFunction(element) {
    element.innerHTML = "You pressed me with a keyboard!"
}

This is a rather simple case, but the point is, it's these countless needless considerations that would make things needlessly complicated. It's just easier to, as a developer, be responsible for your own software.