It's possible but also difficult to jam radio. That's part of why programs like Radio Free Asia[0,1] exist. Even if you can't broadcast from inside a territory you can broadcast from outside. It can be jammed but it is a tough cat and mouse game and jamming isn't precise. So when you jam there are causalities. Not to mention that jamming can be quite expensive.

I'm not saying that makes the problem easy, but I'll say that jamming isn't a very strong defense.

Though the bigger issue here is probably bandwith. It's hard to be both long range and data dense. There's probably easier ways to distribute this. Hell, both Koreas are known to transport different things via balloons.

[0] https://en.wikipedia.org/wiki/Radio_Free_Asia

[1] It is also why projects like Tor and Signal get funding from RFA. Maybe the US doesn't want encrypted services here, but if anything, it's for the same reason they do want encrypted services in other countries.