pins used for Nrf24L01 on a Mega

Apologies for such a simple question, but is there any reason why any of the digital pins on a mega 2560 cannot be used for CE,CS on the NRF24L01? I see that in all examples I've seen the PWM pins are used (typically 7,8), but i don't see why a chip-enable/select would need this capability, they don't need to toggle quickly, normal GPIO capability should be enough for even for framing an spi-packet?

I would like to use pins 45,46 for CE,CS - i'm having some problems and i'm wondering if i don't understand something basic.

The SPI library documentation lists the pins required for the different Arduino boards.

On a Mega, Pin 53 must be set as OUTPUT but it is not necessary to use it for CE or CSN

...R Simple nRF24L01+ Tutorial