Because TCL, as pointed out elsewhere, referenda and general elections differ. So they can't really be compared.
One chooses a government to continue making the decisions we want. The direction it takes us may need balancing after 5 years (or less) with a change of government. Governing is an ongoing process so changes are expected and accepted.
But a specific issue needs a specific decision, and for it to be adhered to, or the nation just flip flops and gets nowhere. Other nations would see our incompetence and take advantage. It's pointless holding referenda if one encourages indecision and going nowhere, especially before the decision has even been acted upon. One does one's consideration first, then one decides, before actually voting. Losing sides delaying progress and making excuses about changing minds can not be tolerated if the nation is going to achieve anything. The decision has been made, it may be reviewed after achieving it, and after a sufficiently long period has elapsed that it can be judged properly; not at the losing party's whim.