there's different installation processes for each product, some are very similar, others not so
the admin web control panels can also be very different, making it hard to find equivalent settings in different products
when you're looking for log and configuration files, they're not necessarily where you expect them to be
I suspect part of the problem is that some products are from a forked common code base which diverged, and the others which were not Atlassian products originally are skinned to look like them, and there's some attempt to make their code base converge with the others.