I had at least 30 first cousins, maybe more, (my parents each had 9 and 6 siblings respectively). Even though we lived no more than about 30 miles from most of them I rarely saw some of them and there are several that I never ever met as we didn't have a car. There were no 'fallings-out', it's just the way it was then! As far as I know they are still alive apart from 3, but I'm only regularly in touch with a few of them. If I sat next to most of them on the bus I wouldn't recognise them!
Of the many cousins that I don't see in real life there are a few I have enjoyed 'meeting' in the past few years thanks to social media and that level of contact suits me. Most of them live a distance away and I don't personally feel the need to travel hundreds of miles to develop the relationships further (although of course it might be different if we all lived nearer to each other as yours may?).
Would it be possible to suggest WhatsApp or Facetime sessions with all or some of them every so often, so that you get together without it being too much of a commitment or too formal? If you gradually built up a relationship that way it might eventually lead to a warmer/deeper relationship with some of them?
Kestrel I'm not sure that this is any help to you at all, I seem to have rambled on, but I will post it anyway in case any of it is relevant!