Why Modern Code is Slow

Because of the entire security nonsense, modern linkers do not support the classic statically linked executables, which were superfast. So all code is compiled the PIE bloatware. Of course that crap goes on top of already slow MMU and meltdown/spectre fixes (which are just an excuse to sell your new CPU). Remember these old COM files? They were ridiculously fast, compared to the modern ELF garbage, where just the header takes more space than the code itself.

Remember: security experts are the consumer's biggest enemies. Common people don't care about security, they care only about apps running fast, liek they used to run in C64.

There's far more to performance improvement than just feature size and frequency scaling. The first few things (not comprehensive) that come to mind: pipelining, branch prediction, cache optimizations. I'd take a modern processor over a 6502 on a new process hitting the same clock frequency any day. If anything these improvements play to your preference for speed over security because they're at fault for all the high profile hardware vulnerabilities in recent years. To get back to the original topic: shitty slow code is nothing new. People used to actually write things in basic on their c64. I believe that there are better tools and more information out there, and the average program is better written today than ever before, but maybe that's a little too optimistic.