@Samantha_Nicole, @Daffy_UK, @helloandyhihi,
Until/if Asana provides this, another workaround (that doesn’t require a third-party tool) is to type Tab +M to “assign to me” anytime after you start creating the task. It’s awfully fast, though you have to remember to do it.
And another workaround: Tab+Q does a quick add of a task and it actually does assign to you by default. But for a few reasons, I prefer the previous approach.
Hope that helps,
Larry