For my kid, the one camp that he attended last month (Mid Major D1) was after they saw him play at a Perfect Game WWBA tournament in Iowa (we noticed one of the coaches watching a couple of his games). He received an email the next day saying they liked what they saw, & could he come to camp. The coach mentioned a couple of specific at bats from the tournament. My son really liked the camp, he got a positive evaluation afterwords and they said they want to stay in contact & follow him.
The other camp invites we've received have been a part of a response after he's sent out emails to recruiting coordinators. In the emails he includes a video (usually of a BP swing or Game swing) & his updated measureables & GPA. Several of the coaches have expressed interest in staying in touch and being updated more in the future, even when he has said he can't make it to the camp.
I get the picture that the coaches like his size, & his swing, and the travel program he is a part of lends some credibility. Everyone wants to see what happens with his measureables over the next 6-12 months to see where he's at, so he's focusing on getting Bigger Stronger Faster.
In general (at least at this stage of the game for my kid, where it is more about getting on the radar of coaches), I like the camps/showcases where a lot of coaches attend. He did one of those in early August, where he met an RC from a different mid major who emailed him right after the camp saying they are interested and to stay in touch. That Coach has said he'll be coming out to a couple of Fall Tournament games this month to see him play.