Bethesda gave them years to pull themselves together, and they could have if they had used those years wisely. Also, the original Fallouts were not pulled from the shelves at all, they just couldn't market any new releases of them or re-package them. Since Fallout 3 came out it caused an upturn in interest in the original Fallouts - they could have made plenty without re-packaging it and little or no advertising. Also, you are assuming Bethesda would have turned them down if they asked, and that is just conjecture.
Say you have a friend who is desperate for money and sells you their nice car. You now own the car. Then one day you look out the window and the person you bought the car from is driving away in it. Would you stop them and say, "Hey wait, that car is mine now!" or would you just say, "Well, it was originally their car, so let them have it," even though you paid them good money for it? By law, the car is yours now, and even though it used to belong to the friend, it doesn't anymore.
The people that "invented" (as you put it) Fallout were the developers that worked for Interplay, not the company itself. All those developers (except Chris Taylor) are now gone to other companies (Obsidion and InXile) - and the reason they left is because they had no control whatsoever over their own great ideas because of Interplay's poor management of the finances of the company.