[Alessi]

But why does it not feel as omnipresent as Love Island did at its peak? It felt so much bigger and inescapable....which was why so many people got such a weird chip on their shoulder about it.

I think you've answered your own question there a little with the phrase 'at its peak". Big Brother had an omnipresent buzz when it was at its peak. But now it's...something different. People are used to what it is, so I don't think it would create a 'buzz' unless something shocking or negative happened. It seems to be successful and I think it can continue to be without it being inescapable. 
I think by it's very nature a celeb version would probably create more of a 'buzz' in some respects depending on who is featured (e.g. if someone like Phillip Schofield took part)