This has been discussed often before. The reason that there's no LTE in a camera is that while there are people who will pay a premium to have a better camera on their smartphone (often bundled with other premium features), relatively few would look forward to shelling out $50+ every month for a big data plan for their camera.It took them until recently to even add basic WiFi functionality to their cameras, some super-basic bluetooth and NFC, typically implemented very poorly with totally inadequate protocol support.
4G/LTE cell capability not present in a single camera in late 2018. Why?! Module available for something like 5 bucks.
I agree that better connectivity with a smartphone would be great. However, it's not going to happen, because neither Bluetooth and WiFi are ideal. Even Bluetooth 5 is only 2Mbps, so a 50MB RAW file would take more than 3 minutes to transfer, under the best of circumstances. WiFi, on the other hand, has the bandwidth, but will suck the life right out of that camera battery, especially if you want your camera to be constantly connected to your phone so that every photo goes straight to the phone. Even so, try tethering WiFi to a laptop, and watch how painfully slow 20+ megapixel photos are to transfer.
For slick connectivity between an ILC and smartphone, we would need a protocol that supported low power idle (like Bluetooth) and high speed transfer (like 802.11ac), that has convenient pairing and reconnection. But if that is developed, it won't be driven by photographers with ILCs, because there are just too few of us.