I'd like to add that it's not always mainly about the chemistry but also popularity. I've seen instances where a member has more chemistry with other members but are shipped with a popular member.
Like previously said, it's the chemistry between the members that sail a ship. It's also the chemistry between members that decide whether or not the ship sinks again. And the more popular the band, the more fans will see this interaction and thus ship it - making it a huge ship compared to smaller groups that won't have a huge fan base to ship a certain pair of group members to begin with.
Because the group they belong to is popular. My ship isn't popular at all, because the group I like is (I think) not popular, and (I think) people hate them. I've been told I'm weird because I like my ship and I seriously hate it.
Most of the time, it's the chemistry between the member :)
Certain, are more obvious than the others, and it's cute ~~~
Personally I love EVERY ship ;)
