I hate that. The last long trip I had, I had one driver. First of all they boxed me in because I could see a lorry a mile off but they were just keeping pace next to my back wheel as I eased off and eased off. They only finally got past when I dropped to 55 as I came right up against the lorry. So I moved out behind them, they trundled past the lorry at 60, moved in, I started to speed up to overtake them and was not really gaining on them, realised I'd go to 85, give up and pulled in behind. With me safely behind they dropped to 60. Three more times I tried to overtake and each time was pushing 90 and still could not get past, and each time they dropped their speed as soon as I pulled back in.
I only got passed them when we hit a bit of more congested traffic and they had other cars to "race" against. But otherwise, it was "I don't want to drive fast, but I don't want anyone in front".
It was not unique either. Over the years I have been driving, I've encountered people like that a few hundred times.