Apple aren't doing this to eliminate malware from their systems. Probably just gearing up to the point where it's impossible to run any application that Apple isn't getting a cut of (or is free).
Realistically, malware only affects a tiny fraction of users, and only a further tiny fraction suffer demonstrable loss from it.
Malware in the past has been an enormous problem, with huge numbers of average users affected. To say that we don't need protection against malware because it's not a major problem now is circular reasoning, and ignores literally decades of effort to bring the problem under control.
For a certain generation of adults, going to visit your non-technical parents socially meant budgeting extra time to eradicate the adware of the month. It was a constant problem affecting large swaths of users, and fixing it was beyond the technical ability of most people.
fwiw, you can disable almost all of Apple's enhanced security features easily on macOS systems.
Their whole design is incredibly neat and well done! If you like these features (or just don't care) the default install does make attacker's lives harder.
But if you disagree with these features or just don't like them you can just boot into recovery mode, authenticate with your password and disable almost everything for macOS.
And if you just like the hardware you can do the same and install a custom kernel like Linux or *BSD and do whatever you want.
You can even have triple boot into one macOS with full security enabled, another macOS install with everything disable and a third "macOS" which actually is Linux.
They spend a lot of effort and engineering time to make all this possible.
Realistically, malware only affects a tiny fraction of users, and only a further tiny fraction suffer demonstrable loss from it.