I'm surprised they (the Borg) don't try to assimilate Earth more often. The Borg would be able to win a surprise attack battle easily. Maybe there are so many worlds to assimilate in Federation space- they just don't know where to start. The Borg are trying to advance their own technology more than acquiring drone bodies. There are races with more advanced tech than Federation.

Earth has something the Borg doesn’t have enough of: humans

Specifically the thought pattern of them, considering, considering that on every one of their invasion attempts, Starfleet just barely managed to win the ensuing battle. I believe humans provide the largest amount of resistance out of every species they assimilated (of course ignoring Species 8472) The Borg probably thinks that assimilating every human will greatly add to their own, and as demonstrated in Dark Frontier, the Borg do not like resistance (specifically the species 10026’s (I think that’s the designation, I just don’t remember the exact designation) one remaining ship with the last few members of the species on board)

I believe that we only see the conflicts with humans. Maybe gives the appearance that they’re obsessed with us. I like to believe they have many assimilation fronts happening at one time that we may not know about.

If they bothered to send more then one ship at a time, the Federation would be speaking Borg by now

Maybe the borg keep trying to assimilate earth because earth poses the most of a threat because of starfleet and the federation.

AND they only send one ship but Seven says they sent a hundred cubes for one planet in the delta quadrant

True. But the delta quadrant is the borgs' home quadrant thus there is more there

In the delta quadrant that is

Good point

But Earth is in the alpha quadrant and the borg are in the delta quadrant so i imagine that it is harder to get ships there.