Genuine question, don't both iPhones and Androids lock out users if they're unable to provide the password? In that case are most of these stolen phones sold for parts?
That's a feature to protect user data not to prevent the phone being reused. Wipe the device and it's brand new (unless the device ID is reported and the phone blacklisted by the networks somehow, but that relies on the owner and the authorities being faster than the thieves, I'd imagine).
Not sure about Apple devices, but for Android there's FRP (factory reset protection). Basically, if an Android phone which has FRP enabled has at least one Google account signed in, after factory reset, the phone is locked unless it signs into one of the Google accounts previously in use.
I cannot find documents about FRP from Google, but here's one from Samsung, and I'm pretty sure it's not limited to Samsung.
I am pretty sure this isn't the case if you report the phone stolen. Your provider will have the IMEI number and can brick it. There are probably ways around this - one that I've heard is that this bricking is regional. If you sell the stolen phone to someone who is going to ship it to Africa, say, and resell it, it would work fine there.
I should say that this info is a decade old, but I knew someone back then who would pay for phones, no questions asked. Also vehicles, even large commercial ones. The containers were going to the Gambia, although I'm sure other people were shipping stuff to other countries and continents. I don't know if bricking is still regional but I've not heard that it's changed.
Another possibility is that thieves are trying to literally snatch a phone out of the hand of someone who is using it, while it's still unlocked. Many of us do banking etc on our phones, and have other login credentials, so perhaps if they get the phone while it's unlocked they can do something with this.
They both have security features to lock out unauthorised users. But there has been a cat and mouse game of hackers finding exploits to bypass the device locks, and platform developers patching them to secure the devices again. There have also been various schemes using rogue employees of phone companies to get illegitimate access to official tools that can unlock devices.
So sometimes the phones can be unlocked. But failing that, there is also a thriving black market for phone parts salvaged for stolen phones.
Many people worldwide have reported that their phone’s location ended up at a specific location in China, where the cell phone parts markets are. Thieves sell the phones in bulk for parts. Obviously that doesn’t account for all mobile phone thefts, but it has become a thing in the US for groups that target big events to steal as many phones as possible to send to China for parts.
Nearly two-fifths of robberies in London last year were for mobile phones, it has emerged, as police warned of rising thefts and insisted technology companies must design out the crime.
Nearly 70% of all thefts in London last year related to mobile phones, through offences such as pick pocketing and taking them from people’s bags and pub tables.
Police hope mobile phone makers will repeat the innovations that made car thefts harder, with industry and law enforcement working together.
Rowley said: “The current practice of allowing stolen mobiles to be re-registered by new users within the phone industry inadvertently enables a criminal market which drives robbery, thefts and violent offending in London.
“We need partners to step up to the plate and work alongside us to break this cycle of violence fuelled by the ability of mobile phones to be re-purposed and sold on in this way.
Khan added: “The spiralling cost of living threatens to exacerbate the drivers of violence and robberies, which we know disproportionately impact young people.
Not really surprising, it's a highly valuable and easily-grabbable item that people often just hold in their hand or leave sticking out of their pocket role walking down busy streets.
I look forward to the introduction of 3-factor authentication. To unlock or reset your phone you would have to transmit a morse code authorisation from your local electric telegraph station.