I was a developer of AAA online games, most of which included F2P models and microtransactions, for nearly a decade. The vast majority of games, outside of select mobile titles, are not designed around monetization schemas - often the monetization schema isn't decided upon until well into development, sometimes as late as the last few months before release and even changes post-launch.
Developers do not design these systems. They are often created and maintained by teams of marketing, finance, and publishing individuals who work directly for the publisher and have very little, if any, direct contact with the actual developers until the very end of development. By which time, the majority of the game's actual content has been locked in and cannot be altered without pushing milestone dates and ultimately altering the launch of the product - which is extremely costly and only happens in the most dire of circumstances (i.e. not because of a monetization schema change).
Lootboxes are often extremely easy to implement and have almost zero impact on the intended progression of the game in terms of altering development. I have never sat in a meeting with other developers and thought about how we could modify the game's natural progression to accommodate for lootboxes - this is across multiple AAA studios, with multiple different publishers, over a decade, across multiple genres, and several different monetization schemes ranging from F2P, B2P, monthly subscription models, and hybrids of everything in-between.
Monetization teams generally just request assets to be used for everything from retailer exclusives, deluxe/collector's edition extras, lootboxes, microtransaction stores, and so on. Often these assets will get additional budget - in both monetary and time resources - in order to accommodate their development outside of the main product, but not always. They do not dictate how the game is developed. They do not dictate how a progression system flows. They do not dictate how other in-game rewards systems are paid out to the player. They often don't even get to choose which assets are created, modified, or set aside for special use cases.
This is how development on these types of titles and these types of microtransactions systems happens. It really isn't an opinion. It's really frustrating to see so many developers come forward and explain how the industry works, from talking to game journalists and publishing stories to writing books about their experiences and how things are made, to developer diaries and podcasts and behind the scenes documentaries and discussions, to online/convention panels and GDC development talks... and no one seems to be listening and continue to spout their ignorant hot takes based on absolutely nothing.
