100m is not a hard limit, but just a maximum limit that Ethernet devices are guaranteed to work correctly. If you have good cables that are terminated correctly, you can actually exceed this limit.
But exactly how much you can push the limit would be an interesting experiment for another day.
I think the reason is more historical than artificial market segmentation. Long ago, the development of Ethernet technologies was targeted to achieve an increase of a factor of 10 for each subsequent generation, i.e. 10m->100m->1g->10g. The need for 2.5Gbit and 5Gbit only came with 802.3ac Wave2 devices, where a Wave2 MIMO AP can saturate a 5G pipe after subtracting WIFI overhead.
Also, 2.5G/5G Ethernet actually did not start out as an IEEE specification, but was started as NBASE-T/MGBASE-T.
From what I remember, the 2.5G/5G/10G devices actually will negotiate to determine the maximum datarate that will work.
Do you think there's a potential for disruption in this market?