A pattern I've started seeing with most "bad" rewrites is that "bad" rewrites are probably usually motivated by burnout than actual architectural problems. People get tired of working on the code, and they would rather be working on something else hence "let's rewrite".
When you hear about "good" rewrites it's almost never framed in a way that is "the old code is bad and complicated." It's usually driven by an architectural need - for example it started in Python, but now we have scaled up and in order to avoid $1MM/month a rewrite in Go/Rust/C would be beneficial.
Or, in the case of changing marketing needs, it can be "we now better understand our customers and a rewrite can help us provide a more stable interface and help us iterate faster". However in this case a full 100% rewrite is never the case and it's usually done piecemeal or by the new system simply proxying requests to the old system.
When the excuse is simply the "code is a mess", then not only are you admitting that the original team failed to design a maintainable system, you are also trusting them to not make the same mistake again. And if their whole motivation is "the code is a mess", they will probably fuck up the redesign, as messy code is a symptom of bad design but not the root cause. If the root cause is burnout, and that isn't addressed, the rewrite may be just as bad.
When you hear about "good" rewrites it's almost never framed in a way that is "the old code is bad and complicated." It's usually driven by an architectural need - for example it started in Python, but now we have scaled up and in order to avoid $1MM/month a rewrite in Go/Rust/C would be beneficial.
Or, in the case of changing marketing needs, it can be "we now better understand our customers and a rewrite can help us provide a more stable interface and help us iterate faster". However in this case a full 100% rewrite is never the case and it's usually done piecemeal or by the new system simply proxying requests to the old system.
When the excuse is simply the "code is a mess", then not only are you admitting that the original team failed to design a maintainable system, you are also trusting them to not make the same mistake again. And if their whole motivation is "the code is a mess", they will probably fuck up the redesign, as messy code is a symptom of bad design but not the root cause. If the root cause is burnout, and that isn't addressed, the rewrite may be just as bad.