I suppose if we knew why we were here it might be OK to ask the question why aliens might also be here. A bit of sightseeing, kill time after a long space flight, hoover up a little culture and then invade? We do make a lot of assumptions about our rights to things and of course when it comes to this planet nobody else has a say (except for the absent gods of Islam and Christianity and they are obviously really bothered about things here right now). Territorially speaking we'll never give up on earth.
The film ARRIVAL is a sci-fi offering that offers the obvious premise that, thanks to that whole Tower of Babel incident 6000 Biblical and fictional years ago we all opted for our own strange and conflicting languages and so plunged ourselves into years of warfare and misunderstanding. This situation was in fact created by the ever reliable Hebrew god for a bit of fun, presumably one wet afternoon when mankind may have been on the verge of actually getting on. If he really did consider the consequences of his actions then he's even worse than I thought - but if you still choose to follow him then good luck to you.
Meanwhile many years later somebody made this interesting film about how our different languages continue to keep us apart and how, no matter what guise they come in, we'll never be able to welcome aliens into our world. As the military tend to manage all the clumsy negotiations in some primary coloured language, you know the script already and we're doomed. You also can understand why any sensible alien just avoids this place altogether, interventions don't play well these days. Probably for the best, concepts like non-linear time, working together and circular, inclusive writing would not catch on with those dumb fucks determined to make America, the UK and the Soviet Union "great" again. Yeah, like back in the real old days, when they first put up the Tower of Babel and people were still fighting over pastures and flocks of sheep.
Below: this means something...