After you've been doing the same thing for, oh, the last 50 years, chances are it would be easier to quit than to find new ways of making the same ol' job seem fresh and relevant. Let's face it: Yeats could be off golfing or gambling or doing any of the other things that retired people do with their days. Instead, he's pegging away at yet another poem – "The Circus Animals' Desertion," which is all about sticking with it until you find the right poetic inspiration. Given the difficulties he's having coming up with any ideas at all, we think he deserves some serious props for the perseverance that kind of dedication to writing must take.
If Yeats were truly perseverant, he would just continue writing poems about Irish myths, because that's where he really struggles.
The fact that this poem is written in ottava rima shows that the old forms of poetry will persevere, even though Yeats's contemporaries had started to chuck them out the window.