People that never worked in the industry greatly underestimate how much it really costs in R&D and production to make a car. Adding "authentication" and "encryption" in this environment is way more complex and has more implications than importing yet another library in a web app.

Even so a few manufacturers go to a great deal of effort to secure their stuff while others are using 20y old architecture because it works and it saves money.

I want to say that "premium" brands are much better, but there are a lot of exceptions. However cars with lower margins and lower overall cost will be worse.