What part of Common Lisp would you consider old cruft and what value would removing it bring to the language that would offset the value we have from having one of the most stable language definitions still in use? I can think of a few dusty parts of the language that are rarely used today but it's perfectly safe to ignore.
Lisp has a good all purpose library ecosystem, it's just informal rather than baked into the language, and I haven't had any significant issues with quicklisp since it came out however many years ago. Writing portable common lisp is not at all difficult and there is no problem like with say Scheme of one library needing a specific compiler. And libraries tend to have a long shelf-life too. How much of Python's standard library is old cruft with better alternative packages available now for example? Didn't they have to prune a bunch of stuff in the python2->3 transition? There is considerable risk in including standard libraries in a standard, and the risk is that those libraries will end up being outdated eventually. You want to add more potential for more old cruft to be in Lisp and then pruned again? Why? Just use quicklisp or one of it's alternatives that are cropping up.
Lisp is not Go, it's an agreement between many different parties about what lisp is, it's not a codebase under the defacto control of one organization, or even an informal group or "community". This is extremely valuable and recent events around Go show why, I am extremely glad that I never payed much attention to Go because honestly I cannot trust it's governance model, but a specification that hasn't been and won't be updated in decades I can trust completely, and if one implementation betrays that trust, I can always move to one of the many alternatives listed in the OP.
sidenote:
> I think every programmer that tries common lisp eventually comes to the same conclusion
if this refers to "Lisp needs more backing from the heavyweights", then OH GODS PLEASE NOOO! I want to write code that will run in a year without modification and won't have some corporation put spyware in my compiler while trying to convince me it's for my own good and have my IDE slurp my code to train some LLM to make it easier to pile even more pointless unmaintainable code upon the world. The "heavyweights" have shown themselves very poor stewards of the discipline of computing indeed.