The "relevant devices" is surely referring to the displays here. I would love to go DP for everything but the best I can seem to find is computer monitors with 1 DP input and usually 2 or more HDMI. For living room type displays you won't find DP at all.
For PC displays on geizhals.eu, out of 3327 products:
157 (4.7%) have 2 DP inputs
2446 (74%) have 1 DP input
724 (22%) have no DP input
Including USB-C ports,
949 (29%) have ≥2 DP inputs
1806 (54%) have 1 DP input
572 (17%) have no DP input
Compare HDMI:
1350 (41%) have ≥2 HDMI inputs
1791 (54%) have 1 HDMI input
186 (5.6%) have no HDMI input
I agree it could be better but I don't think it's as bad as you make it out to be. Looking through the devices that have no DP input at all, 488 of the 572 have VGA inputs, which I'd say indicates an older generation of devices.
"Consumer" electronics (i.e. TVs) is a problem though, I'll agree.
