Bethesda games being buggy is actually not due to this as much anymore, but it is still part of it. The games simply have a lot of issues and a lot of them are engine based, since their engines are frankly relatively unstable and inefficient. In addition they are proprietary, meaning that it is hard to find anyone to work with them that can come in with actual experience, unlike something like Unreal Engine that many companies have.
Due to my experience and situation I have bit more insight to the issues, but I don’t want to share anything beyond that because the information may not be reliable and also may get others in trouble.
However, based upon research that is now public due to investigations from journalists and game pundits and such, I can say that there is a lot to be said about the company making projects without a clear methodology or planning things out well. Frankly, the only projects that aren’t poorly planned or managed are the ones made by their subsidiaries.
Bethesda is just… bad at planning and getting things done right.