May be a daft question but why can’t these tires be used on the front.

If you’re brave enough you can!

I wouldn’t. Not that you can’t do useful things with that level of grip, more than you’d probably be better served by an XC tyre to match weight and durability to the speed and straightline slippyness.

Do you ever need to brake hard? If the answer is no, then crack on.

The lack of central knobby bits leads to low levels of grip in a straight line (hence the low rolling resistance)

You can but what you have to ask yourself is ” do you feel lucky?”

All those tyres are made in a rear tyre specific tread and compound. If you attempt the use any of those tyres on the front, the tyre will realise this at the first attempt to brake heavily and will use all it’s power to put itself at the back, where it belongs, resulting in a 180 degree spin.

No reason at all why you shouldn’t.
XC/Marathon riders are frequently running a ralph on the front which is just like a less burly rock razor. If you are riding mostly trail centre hardpack it’ll probably work quite well.

Agree with Northwind though, if you are riding terrain that would be conducive to one of these tyres on the front, then you are probably better served by some more XC orientated tyres.