That's the nature of the RF business. Most folks are interested in one (<= HF), or the other (> HF), or have money for equipment that handles both. Building good equipment that handles the full spectrum is challenging.

Building that one was challenging too (I used to do RF work for thinkRF). Going back through history, they started off with something that would only cover a specific band (say wifi, or specific cell bands). Then we did the 0440 (400MHz-4GHz), then the 0108 (10MHz-8GHz). There are all kinds of difficulties that come in to making and RF front-end that'll cover all of that bandwidth (we also did amplification and filtering to get better quality reception).

You'll also note the prices, and that those are receive-only devices. Some of the reason the price is so high is that we did all the RF design in-house, designing to our specs. A lot of the cheaper boards out there have less amplification, no (or too little) filtering, and use an integrated LO/mixer/digitizer/baseband chip, which limits them to the specs that chip can handle.

I wonder how hard it would be to modify PyRF for another SDR?

That's all stuff that happened after I left, but I would bet "not hard at all", if you can implement a controller that presents the same API as https://github.com/pyrf/pyrf/blob/master/pyrf/devices/thinkr...