A written constitution doesn't move with the times as the gun laws amply demonstrate. You end up with anachronisms like the right to bear arms that are either interpreted differently by different people (people being people) or used in a way it was never meant to, to justify horrors and legitimise the agendas of groups and individuals that are not interested in the common good.

Also, it's roundly ignored. First amendment? Not if you're black and taking the knee, then you're insulting the flag. The VP can piss away hundreds of thousands of dollars of taxpayers money simply to make the point of a foul liar of a man who sent him on a mission to subvert that very amendment.

The flexibility of an unwritten constitution is preferable, allowing a society to adapt to changes in the wider world as well as things like technology and a million other factors. Societies must move with the times.