You don't have to buy it, but it is reality. You may have owned countless devices over the years but I am guessing you haven't designed or put into manufacturing any of those devices. The OP asked if there was any benefit for the consumer and I explained at least one.
And I explained the biggest reason why companies now make such devices. I'm not going to debate what constitutes "reality" with someone who thinks it's a relative or subjective thing. It's not. Reality is that which does not go away when you stop believing in it. Fact is, no; I haven't designed or put into manufacture any of the countless devices (both cheap or very expensive) which I've owned over the years. But ... so what?
What exactly is your point in bringing up that issue? The cheap devices that I've owned which had battery compartments that their owners could both easily and repeatedly access, exist. You might not like that fact of reality. You might wish it wasn't so. But once again, just because you wish it to go away; doesn't mean it will. My main point which you glossed over completely is that it's not even remotely expensive to built accessible battery compartments into electronic devices. Yes, things such as "... screws, gaskets, assembly line steps, etc., are all real costs."
Yet, companies across the world are still able to put out cheap electronic devices with easily accessible battery compartments;
without major costs passed along to consumers. Sorry, but that's reality. Sitting behind me is a cabinet full of such devices. They still work. I've swapped out their batteries more times than I can remember over the decades. (Yup, decades. Not years.) Cheap radios, cheap handheld Pac-Man games (the one specifically I mean was featured in an episode of "Magnum P.I."), old cellphones. Especially cellphones. I had a basic Samsung with an easily accessible battery that lay dormant for 5 years. In 2009, I was headed to Vegas and didn't want to risk possibly damaging or losing my high-tech cellphone at the time. (Also with an easily accessible battery.) So, I just swapped out the SIM card. Charged the old phone overnight, and I was good to go. If that old Samsung had needed a new battery, I could have bought one myself and installed it on my own for very little outlay of funds. Could have done it in a couple of hours instead of sending it in and (hopefully) getting it back in 7 - 10 days.
Sorry, still not buying that sales pitch about Smartphones costing less simply due to not being able to access the battery. And if it is true, likely we're talking a few bucks at the most. Far from anything significant at all. Despite now preferring to use basic cellphones myself, I used to own the earliest generation of Smartphones. Those had accessible battery compartments. Even factoring in the current rate of inflation, the cost difference today vs. just back then is negligible. It's just not that expensive, not even remotely, to add a cover and a few odds & ends in order to provide a owner-accessible battery compartment. Companies in business are in business to make money. One way to increase profit-margins is to entomb the battery within the device. If the owner needs a new battery, he has to pay over-inflated fees for both a new battery and the task of having the old one replaced. Fees that the company which originally made the device, gets to enjoy. That's just the reality of it.
Once again, you can disagree. Though the reality of it is rather obvious. At least to me. I'm willing to bet that it is to other members as well. I have no problem letting them read our posts and come to their own conclusions.