Is this measureable? Like code readability scores on the GitHub corpus over time?
I suppose it could be quantified by the amount of financial damage to businesses. We can start with high-profile incidents like the CrowdStrike one that we actually know about.
But I'm merely speaking as a user. Bugs are a daily occurrence in operating systems, games, web sites, and, increasingly, "smart" appliances. This is also more noticeable since software is everywhere these days compared to a decade or two ago, but based on averages alone, there's far more buggy software out there than robust and stable software.
The #1 security exploit today is tricking the user into letting you in, because attacking the software is too hard.
Yes, many/most systems now offer some form of authentication, and many offer MFA, but look at the recent Redis vulns -- yet there are thousands of Redis instances vulnerable to RCE just sitting on the public internet right now.
It's #1 one because it's easier than the alternative. But the alternative is also not hard. It's just not worth the effort.