how many people lock their phones for any other reason?

I only lock my phone in case it's lost or stolen, I don't lock it to keep the government out of it, since pretty much everything on my phone is available in Google's Cloud services (except for my password protected password manager), which the feds can gain access to with a valid search warrant.

One. Me.

Huh... why? I mean, burglars and hackers are usually very different people, and the former usually doesn't care about what's on your phone, just your phone. I grant however, that you could have a particular situation perhaps relating to your work which might alter that.

The people stealing it usually want to resell it. They'll wipe it. The hackers want the data on it, esp if they can unlock it, since it might be valuable in itself or connected to your online accounts that they trade on black markets. A subset exists between the two which are people that might target you personally just to snoop, a grudge, incidentally to grabbing information you have on your business that's the actual target, and so on. Best to simply cover each one with whatever protections you need so the attackers' motivations and probability aren't something you need to guess.

You think a thief won't go through an unlocked phone they stole? Even if they don't, the person they fence it to will.

I think whatever is on your phone would be of little or no interest to either party.

Even the dumbest thief has a smartphone and knows it can contain information at least as valuable as the phone itself, and maybe even nudie pics.

The average burglar wouldn't know that, and wouldn't have anything they could do with that information. They're a drug addict who wants shit to fence for a fix. Burglary of the average residence is an insanely stupid crime with enormous risks and penalties.

Thieves sell the phone on to people who know how to exploit what is on your phone to try to get access to your accounts and money.

How would your phone give them access to any of that? All of that kind of thing is inevitably protected by more security layers they won't be able to break, and meanwhile, the phone itself is worth something once wiped. Worse, the longer they fiddle with your phone, unwiped, the longer they risk someone tracking that phone.

They're burglars, not masterminds.

What I heard is phones are often sold off by burglars to organized crime who do know how to exploit the phone to its full potential (and not get tracked, and properly wipe it and resell it after properly copying off the data/login credentials which is sold to another party, which then package the data with other data and sell that, and so on).

Wish I had some better sources. All I could find from a quick google search is that the market rate for full personal info is $20 -- that is certainly something you can get with email inbox access (which is enough to get Amazon login which would have your full address etc etc)

Keep in mind most services only needs your email address and browser cookies for full access, only banking services etc are 2FA.