I'm not sure why it matters why you message some one, given you aren't only maintaining the relationship just to gain from it. I've been in situations like that, took me way too long to realize every time, and left me with even bigger trust issues.
But, so what if I'm bored one day and think... hey, I haven't heard from so and so in a while. I hope they're doing alright, so I message to see. It doesn't mean that I care any less. Life can get busy, and people can be just too exhausted to handle a social encounter, but it doesn't mean that the intention isn't pure or that we don't genuinely care about the other person.
And so what if it's desperation that drives some of us. Who cares how you make your connections, so long as they're real?