Pretty simple really, 10Gbps copper needed new cabling which turned out to be a big hurdle in the real world.
2.5GBASE-T and 5GBASE-T do run over existing Cat5e cabling reliably.
2.5GBASE-T and 5GBASE-T do run over existing Cat5e cabling reliably.
It works fine over Cat6 yeah, but if you've not got that deployed then 2.5Gb or 5Gb is a good step up from 1Gb.