As pps have said; is it about the extent to which they are working royals or the level of threat against them?
It's both.
Many 'ordinary' individuals have threats against them but do not receive any sort of security because, frankly, they are not considered important to national security. As the son of the King, Harry obviously isn't just anyone, but his relevance to the country has declined substantially now that he is no longer representing the Crown and has no honourary military roles.
In other words, the Captain General of the Royal Marines is going to be considered more relevant to the nation than the bloke who twerks in labour rooms.
This is reflected in his current security arrangements. You've yet to tel us quite what is wrong with these, other than that you consider Harry should not have the inconvenience of having to give reasonable notice. That inconvenience should be borne by the highly trained professionals you appear to think should be at his beck and call 8 time zones away. And of course by the taxpayer.
Harry can’t change being the son of the king and the brother of the heir. If I was a terrorist wanting to kidnap someone to promote a cause or leverage funds, Harry or God forbid one of his children,would qualify as a potential candidate.
You might want to pass your insights onto RAVEC. I'm sure they're unaware of any potential threats against Harry, their freuquent high level threat assessments notwithstanding.