EU and Brexit

So the EU has published its draft bill on the UK leaving the EU. Since it was published, the UK pound has lost value against all major currencies. No doubt it will recover, but at the moment the UK seems to be fumbling around over what it really wants once we leave.

Why did we not say the referendum would not be binding unless the majority was x %? As it is the margin of "leave" over "remain" was a small 4%, with almost a half not wishing to leave the EU. I suspect fewer would vote leave now. Many want controls over immigration but still want the tariff-free trade with the EU.