The main problem is the black painted lines on the racing line. Makes it a bit of a lottery. Also, for the team on a tighter budgets it's a nightmare to make enough spares.
It's not so much the amount of water as the painted road markings... specifically the ones painted over in black paint. Hard to see.
I like the idea of 'get on with it' but I can see why the FIA don't want a bunch of teams smashing up their cars and having to spend shit loads of money repairing them.
They did. There was one guy standing in T1 trying to blow a puddle off the track with a leaf blower.
edit: In all honesty, I don't get why they bother making full wet weather tyres. I mean, it seems like every time there's a decent amount of rain it's either cancelled qualifying or 20 parade laps behind the safety car. I wouldn't be surprised if F1 someday becomes a dry weather only series.