Why did Jesus, God, Allah, The Lochness Monster and Bigfoot not actually exist?

I suppose anything can exist in your mind if you have faith that it exists. Problem is that faith is not fact.

because they were never created. well bigfoot might have a chance of existing but not the rest.

Jesus may or may not exist.  There is some historical reference to him, but not until decades later and mostly they were referencing the cult that worshipped him and was becoming a big deal.  The most direct reference is from Flavius Josephus who referred to "James, brother of Jesus".  Which is not exactly killer historical evidence.  But it's not nothing.

God and Allah don't exist because there's no evidence for them AND because the details given for them are logically inconsistent.  No being with all of the properties ascribed to the Christian and Muslim God can exist because it's like saying something is both lighter than air and heavier than air at the same time.  It has to be one or the other.  

The Loch Ness Monster doesn't exist because there isn't enough food in that lake to support a breeding population of predatory plesiosaurs as described AND because we actually know that all of the most famous sightings of him were deliberate hoaxes.

Bigfoot is the most plausible of the things you listed (aside from a historical man named Jesus).  But he's not very probable.  Most likely the sightings are people seeing brown or black bears walking upright from far enough away and at enough of an angle that they mistake it for an upright ape.  Bears do walk upright sometimes.  The hair and footprint samples (aside from the hoaxes of which there have been many) usually come back as bear.  There's alot of forest in the pacific northwest, but the idea that a breeding population could exist there without bones or a carcas or a quality photo having been taken after all these years....it's REALLY far-fetched.  And there are no other primates in that area.  It's beyond unlikely that there would be this ONE and ONLY ONE kind of ape in that region.

What makes you think Allah Almighty doesn't exist? and what makes you think His Prophet-messiah Jesus doesn't exist? Where do you get your information from?