It's far more likely that software is improving, but the tools to break it and the number of people willing to invest the time in learning those tools, is increasing. The fact is there are absolutely untold amounts of bugs in every piece of software every written. Finding those bugs, up until the past decade of automation tools to find/exploit them, has been extremely time consuming with few people patient or curious enough to improve their skills in that arena.

Think about the number of programming frameworks that've come out in the past few years. Or GitHub Copilot and ChatGPT which literally write solid code for you. There's no way software has not improved a lot in the past decade but there are WAY more software devs than there are exploit devs or hackers. Similar to the ratio of lions:wildebeest. Way more prey than predators.