Compare size of fixed-voltage adaptors, to those able to cope with 110v/240v output.
Compare size of fixed-output adaptors to "multi-output" adaptors. Some laptops ones are tiny. All the "generic" adapators are huge.
And that's with a handful of options, maybe 2 options on the input and 3-4 on the output. Now combine sizes. Now add in an input capable of the DC (yes, you can Wheatstone bridge the AC, but that's got to be using diodes big enough for anything you put on). Now add intermediate paths capable of the MAXIMUM current that goes through it, as DC, all the way, down to the minimum voltage (i.e. if it can output 1v, that's going to give 12 TIMES the current that outputting at 12V would give, needing seriously large cables and intermediate circuitry for any practical purpose (even 30W, at 1v, would give 30A ratings... 30A DC @ 1V needs 120mm thick cable for a 1m run).
Even adjusting for "reasonable" voltages up/down, you're also expecting up and down conversion (i.e. mains to 12V and also 12V to 48V), which is rare to see in the same device.
Basically, the thing would be as huge and heavy as a car battery, get fucking hot, be prone to failure, and require internal circuitry and insulation from the power paths that's just not practical. And it would probably be quite inefficient across whole ranges of voltages.
You can't have some tiny 5v chip controlling a variable output of that kind of size without some huge, specialist "break open a UPS and see the kind of size we're talking about" components in it, with thick paths between them.
Honestly, the first thought that comes to mind is "fire", quickly followed by "fucking expensive". There's a reason that you set a standard and follow it and try not to change that standard (hence why half the world refuses to change to the other half's mains voltage). The conversion equipment is then static, and makes it practical. And there's a reason that 100+ Volts emerges as the winner every time, because you can get decent power down a decent sized cable.
Hell, even 12V DC / 240V AC input devices are "rare" in modern life compared to everything else - motorhomes and marine use, pretty much, and expensive and sometimes several years behind the technology. And internally all they do is convert to one or the other, so it's really just a TV and a convertor in a box wired to the same 12V DC input on the actual TV (which almost certainly then boosts the voltage for it's LCD panel) because that's easier to make than some generic device that can take in anything and shove it where it wants in whatever format it wants.
Fuck, even inverters or voltage convertors (110/240V) as standalone devices for generic use are bricks that weigh a ton, cost a lot, and have very limited power output.