Leased lines, MPLS, custom routing setups, hell just a VPN that fails closed. There are so many options for doing this, all more secure that just slapping a device online behind whatever router the cheapest ISP gave you.

The problem is that many of these setups are put behind essentially consumer connections, but with a better support contract or simply fitted with a 5G modem and a SIM card from the cell provider with the cheapest plan.

Building a WAN isn't magic, but it does require working with (competent) ISPs and paying the higher cost.