I don’t think it’s unsociable, it’s more secure and independent.
Four of my dogs, two mixed breeds, one Soft Coated Wheaten and one GSD have been like this.
With the mixed breeds, it was just the way they were, well socialised, calm, confident and preferred their own company. They both curled up happily with our other dogs to snooze, but they were confident, independent and didn’t ‘need’ other dogs to entertain them.
We rescued the GSD when we found her in a terrible state, near death, at around the age of 7 and nursed her back to health. She happily shared a bed with our little Whippet/Sheltie mix, same with my PIL’s Rottie/GSD and Collie mix when she stayed there, but would ignore any dogs she met out and about. She was an older girl who clearly had been through hell and had had to survive on her own though.
My SCWT preferred to stay by my side and throw trick or heelwork to music moves at me, as she loved nothing more than a good training session and would choose that over a toy/ball/other dog any day. She lived with two of our other dogs, but was never one for bed sharing either really. She liked her own space. She was a proper little tart when it came to people though. She’d ignore every dog in the park, but felt compelled to ensure that every single human adored her and was most offended if someone didn’t. 
It makes life much easier to be honest. I’ve had seriously reactive rescues as well and I know which ones I preferred to walk with.
My current old Lurcher lad is midway between the two. When he was younger he would say a polite hello and move on or occasionally, if the mood took him and it was the right dog, agree to play. He did love a good game of chase with our other dogs though. Now he’s an old man he prefers a quick hello and move on, but youngsters tend not to invite him to play anyway these days and we can’t have him off-lead, as his sight and hearing are poor and he tends to try and follow the wrong people home! He’s very popular with new puppy owners, as he’s always polite and gentle and it’s the perfect, meet-greet-move-on situation that helps with positive socialisation.
Having had seriously reactive rescues in the past, I would prefer an independent one every time. It makes life so much easier and walks far more relaxed and enjoyable.