Why is vat collected?

Why is vat collected?
Value Added Tax (VAT) is government applied tax on taxable supplies at different rates most of which is 15% in UK, while lower rate 5% and zero-rate are used as well.

Let's say there is a company A,which manufactures cars and sells it to the distributors.Now the company A will charge VAT to distributor and include on the invoice.
Now A has simply collected the VAT on behalf of government and has the liability to pay the VAT collected back to government.
While the distributor can claim that paid VAT back from the government if the distributor is VAT registered.so by this point, government has actually received nothing,as it returned to the distributor whatever it received from the company A.
Now, when the distributor sells the car to end-user, distributor charges VAT to that end-user and collects the VAT again on behalf of government, and pays the VAT collected to the government.As the end-user cannot be VAT registered, so he cannot claim the VAT paid from the government, so the government has now actually received the VAT inflow.