Today, Airship Syndicate announced the return of its online action-RPG Wayfinder, albeit with a few key differences. Though the game was pulled from Steam while its previous publisher, Digital Extremes (Warframe), was transferring the rights to developer Airship, it is set to land on the storefront again on June 11…
There's a whole field called Marketing Analytics that is dedicated to quantifying the results and context of marketing efforts. It is rare for companies to spend a large amount of money (e.g. on marketing budgets) without some means of measuring what they get from spending it. This measurement generally includes things like impressions, click-through rates, time spent engaging with the content, google searches for the marketed material, visits to the websites, view counts, average and median watch time, and so on. There are a lot of key performance indicators that analysts will track in order to measure how effective a specific marketing tactic is, and those performance indicators get compared to the cost of the marketing tactic to determine overall cost efficiency.
A good rule of thumb when answering questions like "Why don't companies do X anymore?" is to think about what X will cost them and what X will get them in return. The purpose of doing things is ostensibly to generate value - no one does X without a reason. There needs to be a method to determine whether the returns of a choice are worth the costs of that choice in order to make a decision. Let's consider the bigger costs of recording "Making Of" videos, and then consider the gains from releasing those "Making Of" videos.
Producing behind-the-scenes "making of" video requires getting a film crew, recording developer interviews, and setting up + filming B-roll footage of the developers doing things (most commonly animators moving wireframes around). Recording the interviews isn't off-the-cuff either, the developers being interviewed need to think about their answers and prepare as well. The time these developers spend recording these interviews is time not spent doing their assigned tasks or fixing bugs, which comes at a material cost when there's a deadline. These interviews are coming at the cost of bugs not getting fixed.
Next, consider what these videos earn in exchange. When the publisher puts them out, what is the gain? Who will be most interested in behind-the-scenes videos? How can the publishers convert these videos into tangible value? Making players feel good or "exposure" isn't really worth very much. We're giving up a significant quantity of work, we need to get something equally or more valuable in return. One possibility would be making these videos a Collector's Edition pack-in bonus for a retail game. Another value gain could be offering them as a stretch goal for a crowdfunding drive. A third possibility would be paying for this as part of the marketing budget, but this still only really targets the extremely invested audience already and is difficult to convert to tangible value gain.
Ultimately, it's a cost-benefit analysis. Look at the studios and games that are doing such videos and consider what circumstances they're doing them. There's usually some reason that the production of such is a tangible value add and there aren't a lot of them.