It’s not a con (or at least, a few might be, but most aren’t!). There are loads of them around at the moment, it’s a way that companies that organise ‘events’ can generate some income and interest while they can’t run events due to Covid restrictions.
Whether or not they’re necessary is another matter. Some people don’t need medals, likes, kudos, points etc to get out and about, and won’t be bothered. Some find it motivational or a bit of fun. Each to their own.
Several of my friends are doing them. One is doing a ‘300k in June’ challenge. It meant that she dragged herself out to spend yesterday walking a long way in the countryside with me, getting tired, footsore, muddy and rained on, when she could have been enjoying herself. 😉