*I don't know a single Remainer who thought the EU was perfect but they thought
a) it was better to try and change from within and
b) leaving the EU with absolutely no idea of how that will play out was not a sensible option*
The tipping point between voting leave over remain was (a):
Whilst a remain voter thought it 'better to try & change from within', a leave voter's view was that trying to change from within appeared increasingly futile - with 27 other countries required to be in agreement for any change to happen.
Cameron basically being told to trot off back home like a good boy by Juncker weeks before the ref was the final nail in their belief that 'change from within' was in any way achievable.
Whilst remain voters were willing to keep at it, leave voters thought it more prudent to cut & run at that point.
To quote Kenny Rogers:
"You've got to know when to hold 'em
Know when to fold 'em
Know when to walk away
And know when to run
You never count your money
When you're sittin' at the table
There'll be time enough for countin'
When the dealin's done

Every gambler knows
That the secret to survivin'
Is knowin' what to throw away
And knowin' what to keep
'Cause every hand's a winner
And every hand's a loser
And the best that you can hope for is to die
in your sleep"