Sadly (for us family history researchers anyway) there are many people who have their DNA analysed to find out whether they are English, German, Scandinavian, Indian etc - as encouraged by the companies offering the service.
Little do they seem to appreciate how questionable this particular 'where you're from' sort of analysis is.
And then, when they've not really understood the full implications of spitting in a tube, in terms of where the data goes, they get an unexpected email from someone
Some are not interested in finding any more family, they've got enough of them already
Some are concerned at out-of-the-blue messages, and are just waiting for you to ask for their bank account details
Some are too busy, can't think right now, and will put aside for a reply - at which point they forget and then when they remember they feel it's too late to respond.
And some, when faced up with finding potential NPE with relatives just don't want to deal with it.
It's very disappointing, and certainly when I contact people I try and say something very unthreatening, offer to share information and do some joint research, and then say - "but if you're not interested in family history research, no problem, it's great to be in touch with you anyway".
Have I got any better results in obtaining replies - don't think so

- but at least I feel I've done my very best to appreciate where the DNA match might be coming from
Good luck to everyone - family history research is always so frustrating when there are mysteries which you can't believe you'll never be able to solve. But they probably are insoluble, and we just have to get over it.