Not sure you can make them close or that we can make that a duty, but I think we can do things that help or hinder the relationship.
My four kids have very conflicting personalities, but get on very well most of the time, while my siblings and I were pretty similar, but haven't seen each other in over 20 years and were distant as kids.
My siblings and I didn't get on because from a young age we were discouraged from doing so. We were frequently put into competition with each other and adults laughed encouragingly if we belittled each other, we were compared a lot, we were put into a lot of separate activities, and for my younger sister and I, I was basically made responsible for her from when I was about 5-6, and I was also responsible for her friends regularly, and both put her and I at odds. When we did get on, we'd often be scolded for being too loud and separated. My parents prioritised apperances and performance far above relationships, which made things very tense and and when we got older/self-sufficient, they basically gave up and the motto was 'do what you want as long as it doesn't bother us', and because we had no foundation together, we went different very quiet ways. We were also discouraged early from being in the house, so as teens we were generally only home with friends without adults or our siblings around.
I've tried to do the opposite with mine - I priortise the family relationships and activities that can be done together. When they were little, I was strict on how they talked to and about each other - didn't even let them call each other stupid. I'm very clear they're distinct individuals with different strengths and likes, but that we can still find ways to enjoy things together. While my older kids may be asked to do nice things for the younger ones, I didn't make them responsible until the younger ones were self sufficient and the older ones were asking things like 'Can I take him to the park', and still absolutely never responsible for their siblings' friends, not even now my oldest is an adult. My oldest is 19, my youngest 12, and they share hobbies. Our home is fairly open to friends, and they have a general attitude now of 'of course my siblings can be involved'.
My oldest has had times withdrawn away from the younger three - I think COVID hit him the hardest and he fell into a lot of computer use once it became his main education and social method & he has difficulties with communication that can make things harder for him - but we've working on that together, and he's seen he's much happier when he had family time along with his personal time.
Yeah, part of it is chance, but I do think there are ways that encourage good relationships - or at least, don't wedge siblings apart.