I can't prove it but I suspect that when the lower end of the market started having success flogging 3000 watt inverters, the rest of the market was forced to follow suit.
Losing a sale to a competitor makes them stronger and you weaker.
This could be, I wouldn't be surprised, also with the explosion of 'vanlife' and related trends of people building DIY camper/vans/busses etc, I imagine the 12V market has expanded considerably, and many of these people dont really have much knowledge or awareness of the systems they are designing, which I'm sure leads to more demand for high power at 12V.
But on the other hand, I think Victron has roots in the Marine world going back a good ways, and 12V has been common in that world too.
3000 watt 12 volt inverters are the super size option of the inverter market, they look like a good value proposition to first time buyers.
That being said I'm sure there are use cases where a 3000 watt inverter at 12 volts is indicated.
To me, its the far upper end of realistic @ 12V. Definitely beyond optimal, arguably beyond sensible in most cases, but not yet outside the realm of reason if that is where your priorities lie.
2000W @ 12v seems like a more realistic upper limit. And even then after accounting for inverter inefficiency you are looking at upwards of 200A, so even ~1500W could arguably be considered a reasonable top end for 12V.
But I think its also important to consider that, many people size their inverters to exceed what they expect to actually use, and just want to build in some margin for error, etc. In this context, is where I see a high power 12v inverter being semi-reasonable, if you have other compelling reasons to want to stick to 12V, and maybe only intend to use 2/3 of that max, but would rather oversize than undersize. Of course oversizing carries a cost penalty, beyond just the cost of the inverter.
I think you are right though, the bread and butter of the high power 12v market is new and uninformed buyers, attached to 12v due to familiarity (and often pre-existing 12v components/systems) but wanting unrealistic amounts of power. The good ole' 200W of solar paired with a 5000W 12v inverter builds :D