As charper1 said, they have no license to operate - but that really isn't the biggest part of the problem.
The big deal is on reselling copyrighted material.
BEV and Expressvu, like Directv and Dish, own nothing but a distribution system. What they sell is the copyrighted material that they have a license to sell.
Just as CBS has a contract agreement to the rights of CSI in the 50 United States, CTV has a license to it in Canada, but not the USA. Thus, CBS could not pick up, say a Toronto affiliate (assuming the Government of Canada would let them) without re-working all of their programming agreements (again, assuming the Canadian Government would allow a Canadian TV station to be a USA affiliate).
Likewise, CTV has the rights to CSI in Canada - but not in the USA.
While BEV and SC could in theory license anyone within their signal range providing the individual governments would let them, the rebroadcast of copyrighted material is limited to a certain area (Canada) and not the USA.
Directv pays the NFL stupid money for the NFL Package - just read the threads and you will see how many put up with bad PQ and choice from Directv 24/7/365 just because of these 50 games on essentially 20 days a year.
If BEV was able to sell to subscribers in the USA, Directv would enforce its rights with the NFL and BEV would end up with no NFL Season Ticket - as the differences in funding between BEV and Directv to the NFL isnt even close.
Likewise, as the USA license holder would end up enforcing all their rights against BEV or SC if they sold subscriptions in the USA, BEV and SC would in essence be left with purely Canadian Programming. In the trickle down effect, actually, BEV and SC would be left with no programming at all, as the rights holder would pull their re-transmission agreements with BEV and SC - putting it exclusively on cable.
Remember, the USA Network Programming that is imported - as well as the movies for Movie Central and Movie Networks have big rights holders in the USA as well. You think HBO would license The Sopranos to MC and TMN if they could sell it in the USA?
Likewise, HBO, SHO and Starz would hold the big blockbusters hostage (Rightfully so) thus MC and TMN would be nothing more than Stuntdawgs, Artist Profiles and Canadian Movies that are thrown in to meet Canadian Content requirements. That said, MC and TMN would pull their retransmission rights with BEV and SC before they were condemned to that slow death.
So, in essence, the reason they cannot sell to anyone is because they do not have the right to do so.
If they were to sell outside of Canada, the program suppliers that they have redistribution rights with would be force to drop BEV and SC from any distribution of their programming - otherwise, they themselves would get cut off from the rights owner themselves.
It's essentially no different than the DNS issue in the USA which everyone misunderstands and thinks its their god given right to have access to.