Ill make it extremely simple for you.
We'll trade together. You be Britain and I'll be Europe.
Now I'll give you £8 worth of goods today and then you can give me £10 worth of goods tomorrow. We'll repeat this trading of goods ad infinitum...oh hold on I don't want to deal with you any more.
So now you are £2 up and I'm £2 down. Every 2 days. Why would I want to stop trading or dealing with you when I make money by selling you stuff and buying stuff from you?
The idea that Europeans are going to cut all trade off if the UK either leaves the EU altogether or remains in the free-trade area is simplistic naivety at best.
China has no problem trading with the EU. So why does any other country have to be bound by EU employment law in order to trade?
It would seem that you are the one who doesn't seem to understand.
*edited to add - £10 and £8 are arbitrary figures. Just google european balance of payments for figures.
Primarily because of the favourable trade status. We might buy more from the EU than we sell to them won't mean that Europeans will cut off alltrade, but they will reduce it.
Further to that we have the free movement within the EU. If we leave, we lose that. We lose that, we lose the Polish, Bulgarian and other Eastern European workers that do all the jobs in the british farming industry that Brits simply do not do. We lose those, our slowly improving farm industry will tank. Further to that, the immigrant population of this country contributes a great amount to the UK economy. We lose them, we lose out.
Add to that we will lose a large, LARGE number of workers rights and industry regulations. As it currently stands, the EU sets a minimum, if a nation goes further than the minimum they don't have to alter their laws, but if they are under they do. This has led to much improved safety for workers and consumers. In some cases the UK will not change at all because our regulations are further than the EU set minimum. In others we will likely go backwards.
Then of course you lose all the added benefits. The ability to trade with China, the US or other nations as a large block for payment is a huge benefit economically. There's the fact that we woul lose the EU healthcare coverage that means if you get injured or sick in France or Germany or Spain you will get treated. There's the freedom of movement and freedom of working.
As Tomtomkent said before, there are a huge host of reasons being in the EU is preferable to being outside of it, but there are sadly a large number of people in this country who are led around by the nose by some of the despicable anti-EU rags like the Daily Mail who hear the "we pay more" bit and either ignore the multiple benefits or try to cast them in a bad light "We're losing powers to Brussels" being a firm favourite even though it's almost never true.