I'm pretty sure I know what's going on.....
The simplest part of the boombox is the amplifier. They sell them in complete modules now and all you need to do is design a power supply to power it, and voila, instant boombox. And of course we all know that these blutooth receivers are cheap and can be stuffed into a box requiring only a power supply and maybe an external button for pairing. Voila, instant bluetooth boombox. Although in reality, to me, it's not a boombox at all. It's a blutooth speaker.
I mean, everything that we've come to know and associate with boombox, from my era when I was growing up, is lots of controls, the more the better. And every boombox needs a radio and that cool antenna which shows that the unit means business. And of course it needs a cassette player too otherwise, it's just a radio. Then later came CD's too with units sporting AM/FM/CD/Cassette/Line-In... 5 or more functions. And as if a cassette player isn't enough, why not add TWO. Then there's the even that one that has 3 decks including a removable walkman type. And of course that iconic look, cassette player in the middle, tuner dial along the top edge, outboard speakers, telescoping antenna and the carry handle. Knobs, the more the better. Switches, the more the better.
But what has happended? NO CD. NO CASSETTE. NO AM. NO FM. NO ANTENNA and burglar alarm batteries. Oh and an off the shelf SUITCASE HANDLE instead of custom designed pieces for that particular gear. I mean, these look more DIY than a serious piece of gear. When I bring a boombox into the garage, I flip a switch and I got music. For these, YOU must supply the music so your portable device will always be tethered and of course if it's a playlist, then it goes over and over again instead of spontaneous music. With this, I need to decide do I want to tie up my phone and burn the battery or listen to the sounds of silence. Literally.
Why not the other stuff? Because they take a whole lot more engineering to design a box like that and that takes 95% of the entrepreneurs out of the picture. Tuner? Forget it, as that takes a whole lot more technical knowledge and challenge, although FM tuner modules do exist since it's the AM that requires the ferrite rod and FM can be almost single chipped. Almost.
Anyhow, like I said, I'm sure that the diamond box (and other similar type of boxes) do what they do and do it well. If you are having an outdoor party, there's no legacy boombox can touch it. But for a lot of the reasons that Transistorized already stated and the other stuff..... it's not something that I would be interested in now, and at my age, probably never will be interested in.