If RAW doesn't ban him from doing so (and unless we get a more official opinion, it's a matter of interpretation as to whether it does or does not), then yes, there's definitely a pretty big reason why the GM might want to forbid it, and that is the Exploit cyberprogram, which gives +2 to Sleaze when attempting a Hack on the Fly. If you also get Stealth and Edit, and drop Decryption, this gives you 0/1(3)/4(6)/6 - enough to hack small fries and steal their files without using Edge - for 21,580¥, which is less than half what the cheapest Cyberdeck costs you, while also having extra functionalities cyberdecks aren't capable of (namely the whole "make drones kill anyone that tries to go after you" thing). For an extra 330¥ you can add Virtual Machine and Fork, doubling the speed at which you can steal files.