Darin, I think you misunderstand how the data is being connected. Every person (in WikiTree) is a new document that is related to other person through a relationship (meaning an unique id to another document).
So you could be doc #001 and your father could be #002, your mother #003, etc. In order now to find someone in your tree with a DNA test you have to go document by document through the whole tree.
Even if there is a special table that has just the document number for people on WT who did a dna test that will only give the document no, eg #452353. It's not clear to which other person on WT with a DNA test this document is connected unless the algorithm searches one document to the next (going along the connections for each document it looks at).
So every document needs to be retrieved from a hard disk (unless a NoSQL or similar database is used that keeps the most recent documents in memory), making each retrieval a read operation which is costly, especially when you take into account that WT has more than 11 million profiles now. I'm not even counting the number of connections between them, must probably in the range of almost 100 million connections.
Hope you have a better understanding now that such a task / report isn't a small feature to do. Plus, the data at WT is changed every second, new data is added, relationships are added, changed or deleted (through merges).
Don't get me wrong, I'm all in for such a feature and would find it highly helpful, it's just an explanation of what needs to be done. Hope I made it easy enough in laymen's terms.