Those are stupid reasons on Beth's part. For one, there are many, much more inappropriate things for free on the internet. True, none of them have gamesas's name on them, but c'mon, let another website host it if you don't want the heat.
And while I know nothing of programming, it seems like if you have a copy of the game, you have the ability to reproduce it, even if it's harder without the original code.
We are not going to discuss "stupid reasons", because Bethesda can offer any reason or no reason at all, and there is no choice but to accept it. It's their product. They decided not to release it. That's all.
As to reproducing the game, remember that the original is well known for heinous bugs. Supporting such software, even if you don't actively fix the bugs, without the source code is a nightmare. Since you don't program, you don't know how tedious reverse-engineering machine code is. It takes a lot of time and money, and for the game's owner to do so with no expectation of profit would actually be stupid, as opposed to the purported reasons given.