Coding errors are a really common source of fraud unfortunately. You did the right thing but the vast majority don't. Given a choice between admitting the grant money was wasted, the exciting finding isn't real, everyone who cited your work should retract their papers or just covering it up, the pressure to do the latter is enormous.
During COVID I talked to a guy who used to do computational epidemiology. He came to me because I'd written about the fraud that's endemic in that field and wanted to get stuff off his chest. He was a research programmer, assisting scientists. One of the stories he told involved checking the code for a model written in FORTRAN. He discovered it was mis-using an FFI and using pointer values in equations instead of the dereferenced values. Everything the program had ever calculated was garbage. He checked and it had been used in hundreds of papers. After emailing the authors with a bug report, he got a reply half an hour later saying the papers had been checked and the results didn't change so nothing needed to be done.
Little known fact: the COVID model that drove lockdowns in the UK and USA was nothing but bugs. None of the numbers it produced can be replicated. When people pointed out that this was a problem academics went on the attack, claimed none of the criticism was legitimate because it didn't come from experts, and of course simp journalists went along with all of it. They got away with it completely and will probably do it again in future. Even in this thread you can see people defending COVID science as the good stuff! It was all riddled with fraud.
Part of the issue is that scientists are mostly self taught coders who aren't interested in coding. They frequently use a standard of: if it looks right, it is right. The whole thing becomes a circular exercise in reinforcing their priors.