I think when there are mysterious elements, these invite speculation.
With Nicola Bulley, there was her phone on the bench still linked in to a call, and her dog on the river bank.... later, of course, more info was released about her mental health.
With Jay Slater, there's the fact he went off with 2 strangers an hour's drive into the mountains causing the public to wonder for what reason ... later, his murky past was revealed.
With Jack Slater, the person missing in Bristol, he's a clean cut young man with seemingly no mysterious elements or intrigue surrounding him to catch the public's imagination. Personally I suspect he fell into the River Avon as he was quite close to it and sadly every year there's the loss of at least one young person in either Bristol or Bath for this reason after a night out.