The support depends on the amount of display outputs from the display controller. Base m1/m2 has only two, and you need one for the internal display, leaving only one to be routed through thunderbolt or usb-c alt mode. Pro/max/ultra have more of them, so they can support more displays.
Apple devices with base M1/M2 do not support multiple displays even if they were low resolution (thus fitting into the bandwidth requirements), or if you were willing to connect them with separate cables through separate ports. The Displayport encoders are simply not there, and by connecting chiplets into Pro/Max/Ultra, they are.
Is it used for market segmentation? You bet it is. But it is Apple Silicon limitation, not Thunderbolt. As I wrote before, TB3 laptops with Intel GPU had no such limitation, though you had to use multiple cables and ports if you wanted multi 4k@60.
