With collectible card games, one has at least a tangible, transferrable object - meaning if someone wants to sell off their Pokemon/MtG cards, there is a pretty healthy market available. Even if the original manufacturer would go out of business, you would still have the assets.

With DLC gambling (which is what lootboxes really are), however, there are many problems:

1) the device OS manufacturer (Google/iOS) can go out of business, rendering the money one spent on the collectibles worthless

2) the application developer not providing updates for the software to run on new OSes or revoking the software outright, leading to the same result

3) there is no real transferability - at best one can restore their account on a different device, at worst (like in Train Conductor) there is no transferability at all. Moving DLCs across platforms (Android <-> iOS <-> PC <-> consoles) is extremely rare. Selling off the collected DLCs is not possible anywhere.