No, it just makes it harder and feeds a gray market of phone unlocking. You appear to be a person who mostly deals with first-hand hardware in a rich western country, where there are Apple stores nearby.
Most people who sell or give away their devices DO NOT change/reset passphrases. This is true for all devices, and i've often had to recontact sellers in order to obtain such credentials. Sometimes, such communication is impossible, or the owner has forgotten the passphrase after leaving the device for years in a cupboard.
With usual computers, i can usually do without even the BIOS password and just boot on USB to setup a new system. Or at least i can take the hard drive into another computer, set it up and move it back in order to boot. With Apple/Samsung devices i end up piling them in my own cupboard and/or throwing them away, which is OK because i didn't pay for them.
It's infuriating when friends/neighbors came to me with devices they acquired in good faith for a reasonable price (<= 100€ for second-hand phone), and can't get it to boot. They then have to go to a phone store and pay 30-50€ more to get the phone (whether Apple or Samsung) unlocked, through a shady mafia (there's articles online about that). All this because of these evil companies.
> We wouldn't want car thieves (ahem, sorry, "second-hand owners") to be inconvenienced either. (...) While you're at it, perhaps we should require all security safes to be openable with a paperclip
You're making a bad faith argument here. Inconvenience is not the problem. Having to follow procedures to reset a device, changing a car security system because you were sold the car without the keys, or changing a safe lock are all possible though inconvenient. Apple/Samsung make it deliberately IMPOSSIBLE to reuse their device without going through shady third parties.
> You are essentially advocating in favour of crime.
In some circumstances, yes. I'm generally advocating in favor of burning down these Silicon Valley companies destroying our lives and our planet and making billions of the backs of workers. However, in this case i'm merely advocating for the right to repair and the second-hand market, both of which are perfectly legal occupations, at least in my country of residence (France).
I'd like to emphasize that through locking devices to a single "owner", you are essentially advocating in favor of crime, by creating incentives for corruption within iCloud services, while at the same time placing the burden of POTENTIAL theft (which i suspect is just a tiny portion of second-hand devices, though making statistics would be complex as we're talking illegal stuff here) on the good-faith customer who bought the phone on craigslist (or local equivalent) or a second-hand market without knowing it was locked. Yes, most people are that gullible. I don't think placing the cost of unlocking on second-hand owners is fair in any way, or creating any kind of sane incentives on a global scale.
And yes, it's a complete ecological disaster: ask me, i have a drawer full of apple devices (donated to me over the years) to which i don't have passwords. They are essentially highly-polluting paperweights, though i keep hoping they can at least come in handy one day when someone needs a spare part. Speaking of which, locking devices does not prevent scavenging for parts and therefore does not disable theft incentives, contrary to your argument.