As stated in its description https://magento.stackexchange.com/questions/tagged/php the PHP tag is obsolete.
But as you can see there's still 1000+ questions tagged with it.
What can we do about that ? Should we remove the tag from every question tagged with it ?
Deleting the tag would be worse as I'm sure a lot of people will recreate it and the "obsolete" description will be gone, it would probably make it worse.