Because "it's old" and "it's everywhere" also holds for things we can and/or should replace. Else you'd be using the tools they were using not 40 years before now, but 20+ years BEFORE the advent of UNIX still.
Now, except for the convenience of "it's on every linux distro" which is more a theoritical convenience (since it's 2021, we have networking, package managers, provisioning, and other niceties, you can take your tools with you to a new job, or the servers you manage. Do you really want to constrain your toolset to the lowest common denominator lest you have to once in a blue moon log in some non-touchable system for some session and you wont have ripgrep there?.
(And if you're not an admin but a developer that makes even less sense - you're supposed to be in far more control of your development enviromnet).
The "I've used for 40 years" argument either amounts to (a) I don't want to learn something new, even if it's improved (which one can respect, but is not a general argument, as others might want to learn something new), or (b) I think the existing versions are the global maxima of such tool design, or close enough not to matter.
Note that (most likely) the tools you use are already replaced versions of the old UNIX and/or POSIX tools -- namely GNU versions of those, with tons of extra functionality and flags and in several cases different behavior.
Without those a system (I had the displeasure to work in some legacy unices like AIX etc that didn't have them by default, but had the legacy UNIX versions of such) feels absolutely medieval...