What’s the problem?

Genuinely asking- I saw a post about celebrity men and their much younger girlfriends. For example, Leonardo DiCaprio and his gf. There were many negative comments about it. Some were calling it predatory or inappropriate, or whatever.

My question is: if the girl is over 18, and consenting to the relationship, then what is the problem? He finds her attractive, and she obviously is into him too so why should anyone care?