Yoast bile şöyle yazmiş

SEO URL structure

At Yoast, we recommend using a simple and clear permalink structure. Ending your URL with the post name is the preferred method and optionally you can prefix the post name with the category, which results in one of the two following permalink structures:

/%postname%/
And with the category prefixed:

/%category%/%postname%/


Benim sitede /%postname%/ ben bu özel yapiyi kullanamiyorum nedenini bilen çikarmi