This is so, so true. So often when people ask questions like this, they seem to be overestimating the value of having access to the code that they're interested in, and underestimating the expense and risk of open sourcing it.
Very few companies would be willing to just throw the code as is to the world. Usually they're going to want to go over that old code line by line to make sure it's fit for public consumption and doesn't contain intellectual property that they don't have a right to open source. All of that stuff costs money and engineering time and probably legal time as well.
They would also have to have some reason for doing it in the first place, something more than that it could be hypothetically interesting to hypothetical people. That's a leap of faith that few companies are willing to make, and the larger the company, the more people have to make that leap and sign on to it.
Having said that, I also wish that more companies would open source their old code (for academic reasons if nothing else). I just think the reason it doesn't happen more often is for really practical and predictable reasons, and not because those companies are totally oblivious to the idea or because they're evil or anything.
Very few companies would be willing to just throw the code as is to the world. Usually they're going to want to go over that old code line by line to make sure it's fit for public consumption and doesn't contain intellectual property that they don't have a right to open source. All of that stuff costs money and engineering time and probably legal time as well.
They would also have to have some reason for doing it in the first place, something more than that it could be hypothetically interesting to hypothetical people. That's a leap of faith that few companies are willing to make, and the larger the company, the more people have to make that leap and sign on to it.
Having said that, I also wish that more companies would open source their old code (for academic reasons if nothing else). I just think the reason it doesn't happen more often is for really practical and predictable reasons, and not because those companies are totally oblivious to the idea or because they're evil or anything.