It's not about trust because many of them have failed people, but it's about their influencing capability and the gullibility of the people. They idolise celebrities, but of course, the loudness of celebrities is marketing on its own, so people get to know what they sell faster, and that will naturally lead to a high conversion rate, even if they (the buyers) do not idiolise them.
You are absolutely right. It's really not about trust or good reputation. I see people follow fraudsters, rapist, suicide promoters, etc on social media. I wonder why people will be influenced by Andrew and Tristan Tate. These young men are well known for rape and human trafficking.
There is a thin difference between the way influencers and celebrities relates with their followers. Influencers creates a personal connection with tier followers, it becomes as if they are in the same scenario or situation as them. So people with similar interest know ow they feel. But for the celebrities, they barely communicate with their followers, very rare you see them make comments too. They are more focused on maintaining their high profile reputation secured. In the end, influencers build more trust than celebrities'.
Celebrities could easily become influencers. Many influencers these days are sporting, actors, designers, etc. Anyone that is having a successful career in any field can easily influnce people who have interest in such field.