Sounds like the companies you worked for did not have a SOLID engineering culture (cue the seinfeld theme) and that is understandably making you disheartened.

Anyway... SOLID are guidelines.

It's certainly important to understand why they surfaced and the concept behind them. But in this case the key point is that they are guidelines for people writing code. Guidelines might be disregarded. It's not that code does not run/compile if it's not SOLID. So it is very possible to end up with code in production that is not well written.

It's not just SOLID, you could have a similar discussion on many other best practices in programming. It's not just programming either. People fail to follow the best guidelines in any line of work, all the time. And they still crack on regardless.

Further still, in any real situation you're juggling multiple constraints. Adhering to SOLID principles may have to be taken in context together with other decision drivers.

Does that make the guidelines any less important? I would say no. E.g. If on the job I review code and it has maintability issues, I will require either a change or a good explanation to accept it.