One would hope they created a new hostname/IP for each source, but even then it is astonishing that they used the same communication method for so many sources.

> Compare that to one way coded messages over hf radio

Having a shortwave radio in your possession is justification enough to haul you in for questing in some countries.

There is also relatively little "radio traffic" to inspect relative to internet traffic.

Perhaps, but given the volume and variety of modern electronics, it's easier than ever for a receiver to look like something else, at least if you don't crack open the case. An antenna can be harder to conceal, but you can often pick up transmissions by tying into unconventional antennas, like the rebar in a slab of concrete, or a long metal railing. You could probably fit a purpose-built receiver / demodulator for FT8 in a usb stick.

There's still "number stations" broadcasting over shortwave radio.

If it ain't broke, don't fix it?!

Number stations, though, are usually used for things like one-time pads or to send a previously agreed upon command. Detailed instructions are not really what number stations are good for.

time, date, longitude, latitude is just below the length of an average number station transfer

My guess is that this is actually relatively new system that was implemented after the criticisms in the week of the September 11 attacks. One of the stories you keep hearing is that the plot was not discovered in time because agencies were not sharing enough information.