I'm no expert, but as I understand the 2.4GHz band has more lax requirements than the cellular bands, but it's not like ridiculously difficult, it's "just" a matter of money. Especially if you're using off the shelf modules.

But at a practical level, there's really extremely few situations where you actually need a WWAN modem. There's almost always wifi available and if not you almost always have a phone with an internet connection. That aside, a big part of why people make these devices is specifically to get away from always-connected internet devices.

It also may or may not need approval from whichever telco operator you're trying to connect to, and the user has to provide their own SIM and do the legwork to get a subscription. It's just not super practical. Not impossible, but a big pain in the ass for not much benefit.