I am not a big fan of the "thinner at any cost" trend in cell phones, but a user replaceable battery is about the least important factor to me. I carry my phone in my pocket and use it extensively every day. If you can remove a battery compartment I am not going to open for 2 years and make it better in any measurable way -- smaller, lighter, more rugged, better ingress protection, longer battery, more features, or really anything, that is absolutely what I want. Cell phone designs are *insanely* constrained. Manufacturers didn't switch from micro to nano SIM cards for their health. They did it because that tiny sliver of plastic was wasting space that they could use for features their customers cared about.
Yes, it does generate extra waste. But take a look at how much trash you put out on the curb every week. Now think what fraction a 150 gram phone adds to that, even if you replaced it every year. Electronic waste is more hazardous than most household waste, and arguably generates more manufacturing waste than other products, but there is no way that my phone is a material part of the waste I generate directly or indirectly. And when you look at the utility I get from a smartphone, it is about the last place to look to reduce environmental impact. Other people's priorities may be different and that is fine, but I think my experience here is pretty typical of flagship / premium smartphone customers. Last I checked there are still plenty of low end phones with replaceable batteries.
For other products the calculus changes somewhat. Laptops are bigger, I use them less, they stay current longer, and their design constraints are tight but not as brutal as phones. I find non-replacable batteries in laptops annoying, but I still understand the reasoning. By eliminating the battery bay, you make the chassis stiffer and stronger for the same weight, you save weight and space, and you have more design freedom in placing the battery. In most cases, laptop batteries can be replaced at a service center. Its expensive compared to buying an off brand battery from amazon and swapping it yourself, but it is still quite a bit cheaper than a new laptop. To me, this is a totally reasonable compromise.