Hiring is expensive, distracting and having an unfilled position can result in other staff leaving. No good company wants to leave a post unfilled. If you're capable and a good fit for the job nothing is going to stop a company hiring you. No matter what the advert says, if you can do the job and you want to work at the company just apply anyway.

But think hard about whether or not you really want to work for a company that says things like this in their ads, because you probably don't.