I want a URL that's not available. It's inactive, but nobody will help me claim it, so I'm moving my blog to WordPress!
When you pick a URL to publish your Blogger blog, you cannot pick one that's already in use. Blogger lets us publish our blogs to our own standards, as long as we publish within Terms Of Service. Blogger lets us keep our blogs, for eternity, if we so desire - and will not interfere with our plans for eternity.
If you are so determined that your blog have a certain URL - and are so certain that only that URL will do for your blog - you probably belong with a WordPress blog. If that Blogger URL is unavailable, because it's in use by a previously published Blogger blog, then a Google custom domain - or a WordPress URL - is probably your next best bet. Note that both custom domain URLs, and WordPress URLs, are also subject to availability.
Blogger is what it is. If you're not able to wait for Blogger to improve, and your personal needs are satisfied better by WordPress, you'll probably be better off there. Please feel free to go, with our blessings.