title attribute of image elements

I have noticed, when using WordPress, that:

<img src="https://www.externalsite.com/image.jpg" alt="alt" title="title" />

gets rendered as:

<img src="https://www.externalsite.com/image.jpg" alt="alt" />

stripping the title attribute. However, using an <abbr> tag with a title attribute works.

Is there something obvious that I am missing?