Some anecdotal knowledge I can share on why they used to say wait as long as you can for a hip replacement:

We were told this was because it used to be that they could only do the hip replacement surgery once, and the replacement joint would only last around 20 years max.

So basically it had to be for the expected life span of the patient!

But now this is no longer true. Well, in Australia at least with access to modern replacement parts, surgical techniques and specialists!

I could be muddling it up a bit, so happy to be corrected :-)

I recently got told something similar in Europe, and anecdotally anyone who’d had a hip replacement and waited on it regretted not doing it as soon as the doc told them.