[banjo_milkman]

10GBASE-T was actually standardised in 2006. PHY chips were available that year but reaching 100m was very difficult on unshielded cables - the chips were large, high power, expensive to make, 100m was only guaranteed if users upgraded the cables to Cat6A - and the solutions had relatively high latency due to the need for powerful error correction. After PHY vendors had 100m working - an enormous technical challenge - they were not inclined to release an 'easier'/cheaper 10m/30m version, since that would have enabled more competitors, reduced revenues and partitioned the market. But hardly anyone was deploying 10GBASE-T anywhere anyway. So the technology got stuck with low revenues/high prices supporting 100m reach.

Broadcom were making $$ from 1GBASET and were slow to develop/release 10GBASE-T, they held the market back and encouraged SFP+ since they did sell those chips. Intel/Cisco were inclined to wait for BRCM chips. The startups that developed 10GBASE-T (Solarflare initially led, then Teranetics, Aquantia emerged) were not successful quickly. Eventually Aquantia managed to partner with Intel & survived. Both Solarflare's PHY technology & Aquantia ended up being acquired by Marvell, Aquantia for significant $$ last year. Teranetics circuitously ended up as part of Broadcom. The rest of Solarflare was acquired by Xilinx.

10GBASE-T wasn't a good fit for data-centers due to the high power/latency. So those customers went direct attach / SFP+ / optical. Which drove those prices down, and made them more attractive, further delaying 10GBASE-T volumes. Data centers got used to expensive cables, (relatively) cheap/simple low-power, low-latency transceivers. 10GBASE-T was a solution looking for a problem.

Eventually the 2.5G/5G Ethernet for Wifi back-haul opened the copper market up - those technologies reuse almost everything from 10G. Also automotive Ethernet too. Chip/power scaling and increasing volumes for Wifi/ datacenter deployments has eventually driven down the cost to a point where 10GBASE-T is becoming more widespread/attractive.

The initial sales/marketing strategy for 10GBASE-T failed, sadly, and it has taken a long time to recover.