This is simply where the market is converging to at the moment. The typical kit lens is still 18-55mm on an APS-C sensor but most people find wider angle more useful, so some manufacturers made a few lens that start at 16mm. Olympus still sells many of their entry-level cameras with a 14-42mm which is equivalent to 28mm, while the 18-55mm mentioned earlier is equivalent to 27mm towards the wide end.

Fuji also initially and still includes an 18-55mm with many of their mirrorless cameras when sold as a kit. They later made a 16-55mm bright zoom and a 16-50mm kit zoom. Pentax was actually the first one out with a 16-50mm when they launched their DA* line yet they sold before and after many 18-55 lenses. The Panasonic common kit were also 14-42mn, then 14-45mm until they started offering the 12-35mm ones (24-70 equivalent). The 12-60mm you mention is still a more advanced offering.

The same happened with full-frame cameras. My main Minolta film lens is a 28-75mm. Manufacturers made several lenses starting at 28mm (28-70, 28-75, 28-105, etc) but eventually wider lenses started getting more popular and now the 24-70mm is probably most popular starting full-frame lens. Although they have 24-105mm ones that are quite popular too.

Fixed lens cameras slowly evolved that way. 35mm used to be a popular wide starting point, then 28 and now 24mm is the most popular, although there are wider and narrow ones too. Most importantly for a fixed lens camera is that cropping is much easier than stitching, so you want to start with a wide angle that can satisfy most needs.

While lenses are evolving, they are shaping photos we see. I used to find a 28mm wide and now the 24mm (equivalent) seems normal and I use shorter focal-lengths to make my photos feel wide.

At this point in time and for a long while now, the widest rectilinear angle of view are available for full-frame only. Canon makes an 11-24mm lens and IRIX makes a 11mm prime which are both widest available angle-of-view among rectilinear lenses. Previously the Sigma 12-24mm was the widest and it had stay unmatched until Sigma also released an 8-16mm for APS-C. You can get very wide angles but not quite as wide on Micro Four-Thirds with a 7-14mm which is similar to what Nikon offered for full-frame cameras with their 14-24mm.

The field-of-view you get in practice depends on the lens you buy. So if you are going for a general purpose lens, then you can find a 24-70mm or so equivalent for any sensor size. Lenses for larger sensors typically cost more, so going to a larger sensor is costly (even the same is almost always more expensive. If you are buying a lens for its wide angle though, then going full-frame is probably going to cost less for the lens alone. The IRIX 11m Firely costs $525 USD, which is cheaper than the Panasonic 7-14mm F/4 for Micro Four-Thirds and the 8-16mm for APS-C. So at the time of writing, your cheapest widest angle is for full-frame.